If you are in Havana, there are two places where you can get your cell phone operational. One is Cubacel in Miramar (Calle 28 #510, Tel 05-880-2222 or 05-264-2266 for client attention). The other is at the airport, where Cubacel has offices in both Terminals #2 and #3.
See later post on the same subject:
You can either bring your own cell phone or rent a cell phone in Cuba. If you rent a phone, there is a CUC 100 refundable deposit, plus CUC 7/day rental for the equipment and CUC 3/day rental for a line (total CUC 10/day).
If you bring your own phone, it’s only CUC 3/day to rent a line, but you’ll have to take out a minimum of CUC 10 credit to use the phone. Obviously it’s most economical to bring your own cell phone. But to be activated for use in Cuba, your cell phone must be GSM working in the 900 MHz band width or else it won’t work. A tri-band phone is even better.
Cell phones that are CDMA don’t function in Cuba.
SIM cards (pre-paid with a certain amount of time on it) are available from all Cubacel offices and enable you to call anywhere in Cuba and receive calls. These can be purchased for CUC 10, 20 or 40 each.
There are various ETECSA “telepuntos”, including in some hotels, where you can pay the credit charge for using a cell phone.