With the phones that you bought in Cambridge, might they have had area code 289 (instead of 219)? 289 is just the overlay code of the 905 area code. I would not think it was 219. 219 is the area code of northwest Indiana in the USA, but who knows.
Anyways, I know that 7-Eleven pulls stock from one store that is over stocked with phones, to stores that are running out of phones. When I got my SpeakOut phone, it was 416 area code originally, but someone at 7-Eleven wrote another number (with area code 289) on a piece of paper and taped it on top of the 416 area code number.
When I made the first call, it was a 289 area code, so my phone was shipped from Toronto to the 7-Eleven closest to me.
I know you can call SO customer service and change your area code. Read my post about when I changed my sim card from a Calgary area code to an Ontario one. However, I think you got lucky when you said you could choose your own phone number as well. I have made several requests to SO customer service in the past about choosing my own number, and every time I was denied.
They told me that no one can choose, they just get a pool of numbers, and they pick the one that comes on the screen when you call in.