We are planning a trip to Canada this summer. Our cell phone service is limited to US (I think). Will our phone work in Canada or do we need to buy a sim card or phone there to call back to the US?
Depends on your phone, maybe. I actually think all major US phones will work, US and Canada are on the same technology, but not having tried them all I can't be sure. Call your service provider. I do know that Iphones on ATT work fine, but you are charged international rates. I'm pretty sure a friend with a verizon iphone was also able to use hers.
Regardless, you will be charged international rates which are much higher. Options include: plan on minimizing your phone usage OR buy a Canadian phone/sim OR buy an international package. If all you need is to call people at home every once and a while, it's probably best to get the international package. If it's a smartphone and you want to use data, that will add up fast. When traveling internationally, including Canada, I turn off all data and just use wifi. I have a small call and text package for contacting people, but don't use data.
We have Verizon and two kids at Canadian universities who use their American phones. (We do have a plan which covers the US and Canada so I can't say anything about the rates.)
The technology is the same in the US and Canada (same frequency bands, and both GSM and CDMA are in use). So, whether your phone will work in Canada, and at what cost, is determined by your carrier and your exact plan. You should check their website, or with their International customer service (many reports here of regular customer service not being familiar with travel). Or, if you post your exact carrier and plan here, others can help.
If you find your current rates from Canada to the US too high, you can usually get better rates by buying a special plan; often, the plans from Canada are cheaper than the plans from Europe.
Most US prepaid plans like Tracphone, don't allow their phones to work in Canada. Both voice and text:(
I use a TracFone in the US which does not work in Canada, so when I travel to Canada (often -- I live a half hour drive from the border) I use a SpeakOut phone (which doesn't work in the US) from Seven Eleven Canada. You can purchase a phone at any of their stores, but they are not a nationwide chain (Ontario, Manitoba, Saskatchewan, Alberta, and British Columbia only and not everywhere in each province -- no Quebec, Maritime, or northern tier province/territory stores). Air time is good for a year, and you can purchase it at any store or online. To check SpeakOut details, go to www.speakout7eleven.ca/ . Petro Canada (gas stations) has a similar program, but I don't know any details about it. I'm sure you can find them with a browser search.
It would help to have some information on which cell network you're using, what type of plan you have now and what type of phone you're using. It's difficult to say whether your phone will work in Canada without that information.