joE, there is no way that I have figured out t add a P or W but in order to lock the phone go to: menu -> tools -> settings -> Security -> phone and sim and u can set a pin code request whenever you turn the phone on/off or if the phone is left idle for a set amount of time.
Hmmm. I don't really have an answer to your problem. I would put your sim card in a diff phone to decifer if the problem lies within your phone or sim/network. If it happenson a diff phone contact your nearest tmobile/cingular store and have them do further trouble shooting. If the problem lies with your phone contact nokia's tech support. Sorr about delayed response, did not check n73 forums in a while