I don't know about faking the header of the message.

But as for using a foreign line to commit a crime, it is very much possible. A pal of mine from Uganda came to visit and had his MTN line.
The MTN line worked very well in Kenya and he even loaded Safaricom credit. The only difference is the call cost charges are those of international calls

With Regards,
Brian Wangila,
PHP Web Programmer,
Tel: +254728750875,