Subscriber identify modules, or SIM cards, are used in some – but not all – cell phones in the U.S. Additionally, SIM cards for older cell phones may not work well – or at all – with more modern smartphones. When looking to upgrade your phone, knowing whether its SIM card will be compatible with the new phone is important if you want to transfer your existing contacts. If you’re looking to change networks rather than phones, you need to know whether or not your existing phone will even work on the new network. Writer Bio
