so if i buy a simcard from fido or rogers, will it work with any gms phone I buy

unlocked? oh and one more thing i wanted to ask was, do these sim cards have like a expiration date?

If you buy a prepaid sim card they do expire.

Make sure the unlocked phone has the frequency that Fido or Rogers uses.

It should worked.

Most SIM cards have expiration dates when they are not in use.

It will work.

You will need to check with Rogers or Fido which radio frequencies they use, so that when you buy an unlocked phone it can receive those frequencies. Otherwise your phone wouldn't work.

Many GSM phones are triband or quadband phones (meaning they receive 3 or 4 cell frequencies, respectively). 'World phones' are the best because they will work anywhere with a GSM network.