[Sami94]

If I have a data plan but no network connection, as in my room I get no signal unless I sit by the window, if I connect via wifi will BBM still work?

[SwitchBeach]

If you have an active BlackBerry Data Plan (ie BBM is working over the carrier network), then yes, BBM will work over WiFi even if you don't have an active network connection at that moment.

[endevour]

If you have an active BlackBerry Data Plan (ie BBM is working over the carrier network), then yes, BBM will work over WiFi even if you don't have an active network connection at that moment.

actually that is not completely true IMHO
it depends on the carrier service books pushed to your device or maybe (yeah i am not really sure) on the BIS server configuration itself.
On T-Mobile austria I had to call technical support to got wifi-bis enabled for me (even with my bb data plan working flawless over carrier network).
On my BB on A1 (different carrier) email/bbm/.. worked over wifi out of the box.