Calling from St. Maarten / St Martin can be expensive.  The phone systems are not the most up to date and expect to be charged 2.50 or more USD per min. to North America.  Local calls range from 15 to 20 cents per min even with cell phones.  Remember that dialing from the French to the Dutch side (and vice versa) is an INTERNATIONAL call even if you are half a mile away.

The country code for the Dutch side is 721. St Maarten numbers start with a 5, so this is the way to tell a St Maarten number from a number of another Netherlands Antilles island (Bonaire, Curacao...). To call from the US you can dial for example 1-721-555-1212. International prefix is 00 in St Maarten, so to call the US you can dial for example 00-1-212-555-1212 to New York.

The country code for the French side is 590 like for Guadeloupe. The numbers have 10 digits starting with a 0. Landline numbers are always 05-90- followed by 6 digits and cell phone numbers 06-90- followed by 6 digits. When they give you their phone number, some people have kept the habit of telling only the last 6 digits but you have to dial the whole 10 digits (or country code + 9 digits) so you should know (ask if you don't) if it is a landline or a cell phone and add 0590 or 0690 accordingly in front of the 6 digits (or +590-5-90 or +590-6-90). Calling from the dutch side to the french side for diner reservations would be 00 (international) 590 (country code) 5-90-11-22-33 (phone number) = 00-590-5-90-11-22-33.

It is highly advisable to purchase and use calling cards in order to make international phone calls. One of the Calling cards available in St. Maarten is the Irie Card.  These cards can be used from any land line or cell phone and are not limited to Teleshops.  Available in many stores, hotel shops, souvenir shops, car rentals, super markets in the island.  Irie Cards also can be purchased online. Also,  Alosmart offers several calling cards and plans.

You could also rent a cellular on the island, available widely. A popular online source is

 A low cost Voice over IP solution (VOIP) is also recommended, like Calling from your laptop, or from a wifi hotspot on a capable wireless device (like your iPhone) will give you the benefit of $0.02 USD per minute back to the US.  If you want to bring your laptop, this is a cheap and easy way for techies to make phone calls from your room , where wifi is free in many resorts.