I have done a lot of research on this and many many tests to get to this resolution and hence probably a new Database for BlackberryOS to push:
You can use BBM, live Messenger, gtalk, other IMs, browsers and many Apps without having a data plan but using WIFI.
The important part is that you need to have the full service books and you first need to have dataplan at least for a moment to get the service books because that is how you get them either through the BIS webpage or through the Provider Tech department or callcenter; both use BIS to send them to you.
But here is the other way:
have a phone with BIS data plan, re-issue service books to have latest version, use Dekstop Manager (better if latest version) and do an advanced backup and just backup the service books; then upload this to a place where you can list the service books (in .pid format) for all the carriers. This is not phone dependant just carrier dependant.
This will work fine until you cancel you BIS account with your carrier. Then you will no longer be able to use bbm or email in the push format you use now. No matter how you use the phone you must have a BIS account linked to the pin. When we had the days outage even is you connect to wifi you still get no emai or bbm. Posted via mobile device