GSM phones use a SIM card for 2G (voice and text), 3G (voice, text and internet), and 4G (high speed internet and VoLTE) operation. This is a small removable plastic card that stores the data needed to identify a subscriber on a wireless network.
The phone itself is not part of the authentication process; the SIM card handles all of that. Also you can remove the SIM from your current phone and insert it into another compatible device, provided it’s either with the same carrier or you’ve ‘unlocked’ it from its original network for use on another.
Swapping the SIM means the new phone will operate over the same network with the same phone number. GSM is common globally, and is used in far more countries than CDMA.
Phones running on CDMA networks do not use a SIM card for 2G or 3G, but do still require one for 4G. Electronic serial numbers are used to identify subscribers for 2G and 3G. These serial numbers are coded in to the phones themselves, which creates a problem. You will need to get your new provider to grant permission for your device to be given a serial number and thus a working service line and phone number on its network. This permission is not often granted.
CDMA is not nearly as common as GSM in global terms. Travelling with a CDMA phone may be difficult. As for 4G and 3G, both carriers use LTE and HSPA+, respectively.
Canadian networks stopped supporting CDMA phones in May 2016. United States carriers who continue using CDMA after that date include Sprint and Verizon. United States carriers which use GSM include AT&T and T Mobile.
Rogers, Bell, Telus, WIND, Mobilicity, SaskTel and Videotron – run on GSM Network
All networks in Canada cuurently support one or more of GSM / AWS / UMTS / HSDPA / LTE . North American GSM uses 850/1900 MHz , UMTS/HSDPA 850/1900Mhz, LTE 1700/2600, AWS 1700/2100 frequencies. Make sure your own phone is compatible with these frequencies.
You must have a tri-band or quad-band GSM phone, or 3G phone supporting 1900Mhz to be compatible. AWS phones (other than the Google Nexus) are not usually sold outside North America. LTE from outside North America are not compatible but these phones usually have GSM/3G frequencies that are still compatible.
If your phone is compatible, it must be UNLOCKED in order to use a local SIM card. Phones are usually locked so you can only use them with a SIM from the service provider or carrier who supplied the phone. Phones can be unlocked to accept SIMs from other carriers.
A pay-as-you-go SIM card is $10 from most major networks. If you have an iPhone, you can obtain a SIM card from Apple Store in Canada with special pricing. Local calls are $0.30/min and Canada long distance $0.40/min