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Turning 3G off means the phone is on EDGE. If EDGE is not available, then GPRS. If no GPRS, then no signal. So, I guess you don't have EDGE or GPRS in your area.
 
Both Bell and Telus's networks are only 3G. Since they are brand new networks they didn't bother building an edge network.

Only Rogers in Canada has a GSM/Edge network.

Your phone is working correctly.
 
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