I think CR and I have both raved on and on about GoPhone before on this board. With a little more time with mine, I do have one complaint. When you add days/dollars/minutes whatever to a GoPhone it adds to that date and doesn't give you any credit for what you have in the tank. So if you added 90 days when you had 8 left, you would only have 90 additional days on there not 98. .
Yes, it's true that you should renew your minutes before the expiration date. For example, if you purchase $25 worth of minutes, they will expire in 90 days if you don't spend the $25 and don't add more minutes. However, I don't see this as a problem. I put a note on my calendar for one week before the 90-day expiration and I purchase new minutes online even if I have some money/minutes remaining on my account. When I do that, I keep the remaining money/minutes in my account and the new amount gets added.
So if I have $10 on my account when I put $25 in new money on the account, I then have $35 on my account and a new 90 days to spend it. If I have $15 on my account when I renew my minutes for $25 before the next 90 days expire, I will then have $40 on my account. So you can accumulate money on your account from one period to the next if you don't use it all during the current period. I never use all the money in my account and I sometimes accumulate $75 or more in my account. Having extra money in my account allows me to use my phone freely in Montreal and not worry that the per minute charge is higher than in the U.S. You can easily add money/minutes to your phone by buying an AT&T gophone card at a drugstore or by accessing your account online.
Also, if you don't like having to remember to refill your account, you can set up "autorefill" in your online account. And if you add $100 or more to your account, the money will last one year before you need to refill your account (assuming you don't use up all the money on calls/texts).
In sum, the AT&T Gophone is a good deal (in terms of cost and reliability of service) for both Canadian visitors to the U.S. and U.S. visitors to Montreal.