WM6: lost phone service

[usib]

After flashing WM6, I can no longer use my Bell Mobility phone service: all calls that I place are routed to this "You have reached the Bell network, please call Customer Support" answering device.
I guess I'll need to manually re-program the 6700.
I am looking for links to material which explains all this ##XXXX#/ESN/etc business. I don't mind a nice long technical read with a lot of background explanation; but just googling around, there is a wealth of links and I am not sure where to start