The main post office is located downtown of Papeete, close to the sea front. It’s open during the week from 7am to 6pm and on saturday from 8am to 11am.
You will also find some post offices all around the island, as well as in other smaller islands.
As of today, there are 2 operators available : Vini & Vodafone (since 2013)
Both operator use the same GSM 900 Mhz standards and cover around 98% of the population of French Polynesia.
In order to continue using your cell phone during your trip in French Polynesia, make sure that your operator is a partner of Vini.
You will also be able to purchase a prepaid SIM card and get a local phone number for your vacation. More information on the Vini website