blackberry

It all depends on your phone plan.

gert,
one option
you can turn off your cel service & connect to a wifi signal.
you can then send/receive blackberry messages and send/receive email for free thru the internet connection.

one plus of this is you don't have any roaming charges at all.
negatives - no phone calls or access when wifi is not available

Depending on your carrier, you can ask them to switch you to an international data plan for a few weeks/months. Verizon does this. Then you can access the internet and your e-mail. But phone calls are still expensive, US$2.00 a minute (with Verizon). If you only want to talk locally, it's cheaper to pick up a "street" phone ... lots of people have extras that they will "rent" to you. You can buy extra minutes if you need them...

You can buy a phone here with minutes on already for about $12 US, no need to rent one.

If your BB is unlocked, you can just buy a local SIM card and buy a prepaid BB plan for the month, both Claro and Orange offer them. Claro: $995 + 28% taxes, Orange $850 + 28% taxes. That's RD pesos. Both also offers prepaid daily and weekly plans.

There is also a third company, Viva, but their BB service is slow.

Planes Blackberry en Orange Dominicana
Claro - Rep?blica Dominicana
BlackBerry? Viva tu Voz - Nuevos Planes Ilimitados

If your BB is from AT&T, activate with Claro so you get 3G speeds. If your BB is form T-mobile, activate with Orange to get 3G speeds. On Claro you will also be able to use your BB with open APN (for apps and for tethering). Orange does nto allow it on prepaid plans, and neither does Viva.