The +1670 country code connects you to the Commonwealth of the Northern Mariana Islands (CNMI), a chain of 14 islands in the western Pacific about 200 km north of Guam. Saipan is the capital and most populated island, followed by Tinian and Rota. CNMI is a US territory, so it uses area code 670 within the North American Numbering Plan (NANP) — the same system as the US mainland, Canada, and other territories like Guam (+1671) and the US Virgin Islands (+1340).
Despite sharing a dialing format with domestic US calls, calls to CNMI from the mainland are typically billed at international or long-distance rates by most carriers. CNMI has about 50,000 residents, with a mix of Chamorro, Carolinian, and Filipino communities. Tourism from Japan and South Korea has historically been the primary industry, though it has declined since the 2000s.
Quick answer: The CNMI country code is +1670 (area code 670 in the NANP). Local numbers are 7 digits in the format XXX-XXXX. There is no trunk prefix — from within CNMI, dial 7 digits for local calls or 1-670-XXX-XXXX for full format. Mobile and landline numbers share the same 670 area code.
How to call Northern Mariana Islands: quick reference
Because CNMI uses the NANP, the dialing format is identical to calling any US area code. From within the US or Canada, dial 1-670 plus the 7-digit number. From other countries, use your international access code followed by 1-670 and the local number.
| Calling from | Dialing format |
|---|---|
| US/Canada mobile | 1-670-XXX-XXXX |
| US/Canada landline | 1-670-XXX-XXXX |
| Japan | 010-1-670-XXX-XXXX |
| Australia | 0011-1-670-XXX-XXXX |
| Guam | 1-670-XXX-XXXX |
| CallSky app | +1670 XXX-XXXX |
Understanding Northern Mariana Islands phone numbers
CNMI phone numbers follow standard NANP format: a 3-digit area code (670) followed by a 7-digit local number (NXX-XXXX). The full international format is +1-670-XXX-XXXX.
Number structure
All CNMI numbers — mobile and landline — share the 670 area code. The first three digits of the local number (the exchange code) sometimes indicate the island or type of service, but this is not a strict rule. Common exchange prefixes include 234, 235, 236 (Saipan), 532, 533 (Tinian), and 532 (Rota).
Mobile numbers
Mobile numbers look the same as landline numbers: 670-XXX-XXXX. There is no separate mobile prefix like you would find in non-NANP countries. You cannot tell from the number alone whether it is a mobile or landline.
Landline numbers
Landlines also use the 670-XXX-XXXX format. Government offices, hotels, and businesses on Saipan typically use 234-XXXX and 322-XXXX exchange codes.
Mobile carriers in Northern Mariana Islands
IT&E
IT&E (IT&E Overseas, Inc.) is the largest carrier in CNMI, providing mobile, landline, and internet services across Saipan, Tinian, and Rota. They offer 4G LTE coverage on all three main islands and have been the largest provider for decades.
DOCOMO PACIFIC
Formerly known as PTI Pacifica, DOCOMO PACIFIC is a subsidiary of NTT DOCOMO (Japan). They provide mobile and broadband services and are the second-largest carrier. Their Japanese parent company connection made them popular with the territory's Japanese tourist and business community.
iConnect (formerly Choice Phone)
iConnect offers mobile and internet services as a smaller third carrier. Coverage is primarily on Saipan, with more limited service on Tinian and Rota.
Don't confuse +1670 with nearby codes
Since CNMI's +1670 sits inside the NANP, it is easy to confuse with neighboring Pacific territories that also start with +1.
| Code | Country/Territory | How to tell apart |
|---|---|---|
| +1 670 | Northern Mariana Islands | Area code 670 — Saipan, Tinian, Rota |
| +1 671 | Guam | Area code 671 — one digit higher, separate US territory 200 km south |
| +1 684 | American Samoa | Area code 684 — South Pacific, much farther away |
| +676 | Tonga | Standalone country code (no +1 prefix), independent nation |
The most common mix-up is between +1670 (CNMI) and +1671 (Guam). Both are western Pacific US territories near each other, but they are separate phone systems with different carriers and rate structures. Double-check the fourth digit: 670 is CNMI, 671 is Guam.
Time zone considerations
CNMI uses Chamorro Standard Time (ChST), the same time zone as Guam: UTC+10 year-round, with no daylight saving time.
| Your location | When it is 10:00 AM in CNMI |
|---|---|
| US East Coast (EST) | 7:00 PM previous day |
| US West Coast (PST) | 4:00 PM previous day |
| Japan (JST) | 9:00 AM (1 hour behind) |
| Australia East (AEST) | 10:00 AM (same time) |
| Philippines (PHT) | 8:00 AM (2 hours behind) |
The 15-hour gap from the US East Coast makes scheduling calls tricky. Your best overlap is early morning CNMI time (8-10 AM) which corresponds to late afternoon/evening the previous day on the US mainland. For Japan, the 1-hour offset makes business-hours calls easy.
Communication in Northern Mariana Islands
Business hours and etiquette
Government offices and most businesses operate 7:30 AM to 4:30 PM Monday through Friday, following the US federal schedule. Retail and restaurants often have extended hours. English is the official language of government and business, though Chamorro and Carolinian are also spoken widely. Filipino languages (Tagalog, Ilocano) are common in everyday conversation given the large Filipino workforce.
Network quality
Saipan has reliable 4G LTE coverage from both IT&E and DOCOMO PACIFIC. Tinian and Rota have more limited coverage, with some areas restricted to 3G. CNMI connects to the outside world through the Atisa submarine cable and satellite links. Call quality to the US mainland is generally good, though the long distance can occasionally introduce slight latency.
Messaging habits
Given the large time zone gap with the US mainland, many CNMI residents rely on messaging apps like Facebook Messenger and WhatsApp for asynchronous communication with family stateside. Voice calls still matter for government and business, but casual communication has shifted heavily to text-based apps.
The Northern Mariana Islands diaspora
Where they went
As US citizens, CNMI residents can move freely to the US mainland. The largest CNMI communities outside the territory are in Hawaii, California (particularly San Diego and the Bay Area), and Washington state. Guam also has a sizable CNMI-origin population given the geographic proximity and shared Chamorro heritage.
Why they call
Family ties remain strong. Many CNMI residents who moved to the mainland for education or work keep regular phone contact with family on Saipan, Tinian, and Rota. Major calling occasions include fiestas (village patron saint celebrations), funerals, and holidays. The garment industry that once employed thousands of contract workers from Asia has largely shut down, but Filipino workers in other sectors still call family in the Philippines regularly from CNMI numbers.
Dialing examples
Calling a Saipan hotel from the US
The hotel's number is 670-234-1234. From any US phone, dial 1-670-234-1234. It looks just like a domestic long-distance call, but your carrier will likely apply international rates.
Calling a CNMI mobile from Japan
The mobile number is 670-285-5678. From Japan, dial 010-1-670-285-5678. The 010 is Japan's international access code, and the 1 is the US/NANP country code.
Calling a Rota landline from Australia
The number is 670-532-9012. From Australia, dial 0011-1-670-532-9012. Use 0011 (Australia's international access code), then 1 (NANP country code), then the full 10-digit number.
Calling CNMI from Guam
From Guam (+1671), calling CNMI is like calling another US area code: dial 1-670-234-1234. Both territories share the NANP, though carriers may still bill it as inter-territory.
Common mistakes to avoid
Assuming it is a free domestic call
The biggest mistake: because CNMI uses +1 like the US mainland, people assume calls are billed as domestic. Most US carriers charge international rates for 670 calls. Check your plan before dialing, or use a VoIP service like CallSky where rates are listed upfront.
Confusing 670 with 671
One digit off sends your call to Guam instead of CNMI (or vice versa). Both are western Pacific US territories, but they have different carriers, different local numbers, and potentially different rates. Always verify the area code.
Forgetting the time zone gap
CNMI is 15 hours ahead of US Eastern Time. If you call at 2 PM EST, it is 5 AM the next day in CNMI. Plan calls for your evening if you want to reach someone during CNMI business hours.
Expecting coverage on all 14 islands
Only Saipan, Tinian, and Rota have reliable cell coverage. The other 11 northern islands are mostly uninhabited or have minimal infrastructure. If someone is traveling to the northern islands, they may be unreachable by phone.
Prefer calling over WiFi? See our guide to the best apps for WiFi calling.
Frequently asked questions (FAQ)
What country uses the +1670 code?
The Commonwealth of the Northern Mariana Islands (CNMI), a US territory in the western Pacific. The main islands are Saipan, Tinian, and Rota. CNMI uses area code 670 within the North American Numbering Plan.
How do I call the Northern Mariana Islands from the US?
Dial 1-670 followed by the 7-digit local number (e.g., 1-670-234-1234). The format is identical to calling any US area code, but most carriers bill it at international or long-distance rates.
Is calling CNMI the same as a domestic US call?
Not usually. While the dialing format is the same, most US carriers classify calls to area code 670 as international. Check your plan or use a VoIP service with published CNMI rates to avoid surprises.
What is the time difference between CNMI and the US mainland?
CNMI uses Chamorro Standard Time (ChST), UTC+10 with no daylight saving. That is 15 hours ahead of Eastern Standard Time and 18 hours ahead of Pacific Standard Time.
What carriers operate in the Northern Mariana Islands?
The main carriers are IT&E (largest provider), DOCOMO PACIFIC (formerly PTI Pacifica, subsidiary of NTT DOCOMO), and iConnect (formerly Choice Phone). Coverage is strongest on Saipan, with limited service on Tinian and Rota.
Read more about calling other Pacific island territories: Guam (+1671), Palau (+680), and Micronesia (+691).