Easy
Go to the CODETEL office corner of J.P.Duarte and Estrella Sahdala, and sign up.
IF you already have a phone that is. In fact, if you have a phone, you can do it by calling 221-1111.
IF NOT, then you are talking a few thousand pesos and a couple of weeks. You can calculate about $RD1000-1200 per month for phone and internet service.
IF you are on the internet a LOT that is a fair budget.
IF you are a student, and only going to be here for a while, you might have a bit more of a problem--students tend to leave phone bills when they flunk out...and CODETEL is weary..of trying to collect.
good luck,
HB