By APN do you mean Access Point Name? I hadn't set it explicitly, right now it's "internet.com", not encouraging . What should it be?
I checked into that before. When you activate the phone the automated service assigns you one of their numbers. After that you call customer service & they arrange your number transfer. I won't be going through that for a while, my current contract has a ways to go. I'm just forwarding my calls to my SpeakOut # for now. A waste I know, but my phone is my N900 now .