[merlysys]

I am shopping for a used BB9900 and the sellers say their phone can work on all carriers once unlocked. I am in Canada (Toronto area) where we have
Bell
Telus
Rogers

Wind
Mobilicity

I also read that a given phone can EITHER work on the first 3 or last 2 but not both.

Someone told me that if a phone works on Wind/Mobilicity it will work on the first 3, but not vice versa.

Is there a website to clear the confusion?

[NJBlackBerry]

Here's the deal - the phones have different 3G/4G bands. The radios are different.
You can force a Wind branded phone to work on the top three, but all you will have is EDGE (slow) Internet.

Your information is correct.

[dc/dc]

The difference is in the 3G radios. A 9900 from Wind, Mobilicity, or T-Mobile USA will not operate on Bell or Telus at all (it will always be in a roaming state), but it will operate on Rogers 2G. An unlocked Bell, Telus, Rogers, or AT&T USA 9900 will operate on any of those three carriers, but not on Wind or Mobilicity (it will always be in a roaming state).

Hopefully that clarifies a little bit, but you'll really need to know what carrier the device was on before, and what carrier you want to use.