Apple has expanded its list of RCS-compatible carriers, but a few high-profile companies are conspicuously absent.

What's more, you might not even get the other perks of RCS on your iPhone, since the protocol is carrier-dependent. At launch, only the major carriers—AT&T, Verizon, and T-Mobile—supported RCS.

If you've ever noticed a menu for Carrier Settings on your iPhone or have seen a pop-up prompting you to update those settings, you may have wondered what they are ...

Apple finally brought RCS support to the iPhone this year, but the company has to manually approve each carrier ...