You can forward your call to any numbere you'd like. If it's a toll number (int'l) you'd have to pay charges. Otherwise it's minutes.
Any GSM network (like T-Mobile):
Forward All Calls
- Activate *21*[Phone Number]#
- Cancel & De-register ##21#
- Cancel & Retain #21#
- Status *#21#
- Re-establish *21#
You will then have to figure out where to forward to. I'd suggest looking at VOIP options. Not sure if you can do it via Skype In/out, but I bet there are some others which allow cheap call xfer.