Sony Ericsson Z300a in Canada

My Mom recently purchased a Sony Ericsson Z300a Gophone from Cingular, works fine in the US. When she visited Canada it gave a message about GPS and would not work unless she was near the US border(assuming it connecting through the US). It appears that the GSM specs are in synch betwwen the US and Canada, per the Cingular product page the phone uses "850/900 MHz GPRS networks". Any insight as the why it doesn't work in Canada?

Thanks,
Mark

Probably because it was picking up a signal from Rogers/Fido.