You did well by coming here before purchasing.
Please read this first >> Buying a BlackBerry off eBay - BlackBerryFAQ
. Even if it's not purchased thru eBay, they are still good rules to follow.
Also, you will get "all" blackberry services if your carrier provides a BIS / blackberry data plan and you sign up for it which will be an additional cost. BB messenger works with the data plan.