If you had one given to you then activate it on verizon postpaid with a month to month contract. There is no deposit and no commitment if you ever want to stop you tell verizon to cancel and service will stop at the last day of your bill cycle with no other charges unless you have any usage charges. Thye only reason for a contract is a subsidized phone if yopu already have a phone then no need for the contract hope that helps.
There were rumors that Verizon prepaid was going to launch Blackberry Plans back in April. http://www.boygeniusreport.com/2010/01/26/verizon-wireless-lining-up-to-offer-prepaid-blackberry-pla... Never happened. But Verizon is starting to take prepaid more seriously and Blackberry /Rim is cutting deals with all manner of prepaid carriers. Metro, Cricket, Boost and Virgin Mobile all have Blackberry plans now. It is rumored that Verizon reseller Straight Talk will get a Blackberry soon. Verizon is trying out a $49.99 unlimited talk/text plan in the Southeast as a (limited) trial and they are supposed to be launching a five gig (unlimited) data plan this month on their prepaid broadband data menu.
The rumors of April failed but with all this other activity, anything may be possible. If they allow bring your own phone, and it can be added to any plan, monthly or by the day, it will be a huge hit.
Blackberries use the least amount of data among all the major smartphone OSs so I don't see Verizon being as stressed as say launching a prepaid Android would be. Androids use on average of about ten times more data then the typical Berry user.