This should preferably be worded as:
1. Any unlocked GSM phone will work on SpeakOut
2. Any locked Rogers phone will work on SpeakOut
3. A locked FIDO phone may or may not work on SpeakOut depending on phone model and vintage (same network but different carrier lock to Rogers)
4. Some unlocked GSM phones branded to a plan such as Petro Canada will continue to show that company's logo on startup when used with SpeakOut SIM (no big deal)
So in OP's case, simply look for any basic Rogers, SpeakOut or Petro Canada phone to be on the safe side.
(Can't tell by looking that a non-Rogers GSM phone is unlocked, nor can you depend on what the original owner tells you.)