GT-SIM trouble

[Przemolog]

Originally Posted by GSM_student

hummmmm... Simple..Thanks

Well, many national and international SIMs use USSD codes to trigger callback in roaming. The main difference is the format of the number to be called - international but may be preceded with 00 or + or possibly something else before the country code.

See here for examples for Manx SIMs:
http://www.sim4theworld.com/usefullinfo.asp