I'm back in the UK and would like to thank all those who responded to my original post.

I found the variety of cards available bewildering. For example, at the Seven Eleven store near my hotel on Davie, I found cards which were better for long calls (because of set up fees) as well as many which quoted, for example from 3 cents per minute to the UK with no further detail. Very confusing!

In the event, I stuck to text messaging. It appears that Rogers is the only operator which uses GSM and I was able to use my UK T-Mobile SIM on Rogers' network for 40 pence a message (around 70 cents). I received text messages at no cost.

Once again, many thanks for the advice.

P.S. Does the Super Valu chain sell the President's Choice/Loblaw card?