A rather interesting bug has been discovered: emoji sent over SMS between Verizon iPhone and AT&T iPhones is not recognized both ways - Verizon can receive from AT&T, but not vice versa.
When a Verizon iPhone texts emoji to an AT&T iPhone, all that is received is a bunch of random characters. However, a Verizon iPhone will recognize emoji sent from an AT&T iPhone with no problem. This inability to interpret emoji is only an issue with the messages app, however. An AT&T iPhone can recognize emoji elsewhere, like email and twitter, just fine - even if the emoji was sent from a Verizon iPhone.