well if you want to be a rogers customer, there are a few things you need to ensure when you buy the phone off ebay-
1-make sure its unlocked or that the seller bought the phone from rogers in the first place or else you would have to pay to unlock it.
2-ofcourse, make sure its a gsm phone(the one that uses sim cards)
make sure u buy a good phone from a reliable seller. Also you dont even need to ask rogers to activate anything. Just take the sim card out from your old broken phone and put it in your new UNLOCKED phone and your good to go.
Also it needs to be 850mhz capable and not 900 MHz capable as the gentleman above me has specified. it will work on 900Mhz as well but your network connection will be very crappy.