To answer the original question, your best option probably to get a SIM card from a prepaid carrier (so you're not being overcharged for your roaming use) and then get a separate long distance solution. Why 2 separate parts to the solution? Because all the cellphone companies in Canada love to overcharge their customers for long distance charges.

In regards to your SIM card, your options are Speakout, PetroCanada Mobility, Rogers, and Fido. Bell, Solo, Telus, Koodo, Virgin Mobile, and President's Choice Mobile use CDMA and won't work with your GSM phone.

With Rogers and Fido, the SIM card will cost you $35. They have a variety of different price options for prepaid, but the one disadvantage is that the airtime expires after 30 or 60 days, which probably wouldn't work for you. (Rogers does have an option where the $100 airtime takes 1 year to expire)

With PetroCanada Mobility and Speakout you cannot buy the SIM card separately from the company. You can either buy a SIM from someone on this forum, or you can buy an inexpensive phone which includes a SIM. Phones (with SIM and $5 airtime) start at at $59 at PetroCanada and $74 at Speakout. Unfortunately for you their low-end phones only have the GSM frequencies that work in N.America so you won't be able to use it in the UK. The advantage of PetroCanada and Speakout is that the unused prepaid airtime doesn't expire for 6months to 1 year (respectively).

With the long distance part, you have 2 options. You can either buy a prepaid long distance card or set up an account with a service like YakCell. With both of those options, you have to call a number, type in a code, then dial the number you want to call. The prepaid card is easier to set up, might be a little cheaper, but then you have the risk of it running out in the middle of a call if you run out of money. With a service like YakCell you have to have it set up ahead of time, but once it's set up you don't have to worry about it except to pay the bills.

Bear in mind, with both of those services you can use them with any phone, not just your cellphone. If you use it with your cell, you will be paying for local airtime in addition to the long distance charges.

Hope this helps. If you're still not sure what to do, tell us how frequently you travel to Canada, if you stay in the same city each time, and how often you'll be making phone calls when you're here.

isobel,

Don't forget that, unlike the UK, when someone calls your cellphone from the UK, they are not charged extra because they are calling a cellphone instead of a landline. The long distance rates for calling a cellphone are the same as calling a landline.

However, if you are receiving the call, you are charged the regular per-minute rate of usage. IMO this way makes more sense, since the person receiving the call is the one paying for the convience of using a cell instead of a landline.