Blackberry messenger question?

heey, basically i have a bold 9700 and im on pay as you go, and i swear bbm is �5 a month, but ive been getting internet and bbm free all this time? is this a glitch? i havent topped up since i got it because i get it free, i have no texts and i was thinking of topping up but if its a glitch will the free bbm go? my friend said its because of 3g, thats why its free but why would they give their main service for free? i have an 02 pay as you go phone unlocked and i asked their advisors and they said this sint possible! its really confusiing -_- and if i top up, which i havent done since i got it, will the free service go? help? appreciated :)