Unless you want to age prematurely from stress and aggravation, I would strongly suggest NOT to consider VIVA as your Blackberry service provider (hint: no speed at all, slower than 28.8 k dialup in 1995).
Your choice will be between Claro and Orange.
If your BB is from AT&T you should go with Claro as you will get enjoy great 3G speeds (850 MHz UMTS band). You can also go with orange but on AT&T's BB you will only get EDGE speeds. Orange's EDGE network is pretty good though. However, if you go with Claro you will be able to tether with your laptop. Now I use BB with the "social" plan and not "full" I get email, I get web via Opera Mini, and I get tether for my laptop, and it is 50% less than BB Full from Claro (RD$25 per day with all taxes).
If your BB is from T-Mobile USA you should go with Orange as you will get great 3G speeds (900 MHz UMTS band). You should NOT go with Claro using T-Mobile USA BB, because you will only get EDGE speeds on Claro and Claro's EDGE network $uck$. Orange does NOT offer tethering on their prepaid plans.
I say it always - for prepaid BB it's better to go with Claro, but ONLY if you have 850 MHz UMTS 3G phone.