Thanks in advance for anyone's help.

SHORT SUMMARY:
When my phone is connected to WiFi, I'd like to disable any AT&T inbound phone calls. When I'm not under a wifi connection, I'd like to enable AT&T inbound phone calls. This needs to be an automatic process.

LONG DESCRIPTION:
I am trying to leverage the cheap $3 unlimited call option Skype offers. I use google voice, so any time anyone calls my GV number, I can forward their call to multiple numbers. I'd like to forward all calls to both my AT&T number AND my Skype phone number. When I'm on my wifi, I'd like to answer on Skype and use my unlimited minutes. However, when I am out of wifi range, like the car or grocery store, I cannot receive these calls through skype, thus I'd like to then use AT&T minutes.

THE PROBLEM:
The reason this matters is because if AT&T calls are not disabled, then I cannot answer via skype. The inbound call notifier trumps my Skype notifier. Even when I decline the AT&T call, it is nearly impossible to still answer the call through skype.

My device is a jailbroken iPhone 3GS, running iOS 4.2.1.

Any ideas or suggestions guys?