Periodically, text messages seem to hang for a long period of time in the "sending" status. Then I get an error message that says the message failed to send. When I check with the recipient, they usually say they did receive the message. Sometimes they say they received the same message three times.
I cannot see a pattern for when these failures occur. It has happened when I have one bar and when I have 4 bars. It has happened when I'm connected to 3G or 4G, and when I'm connected to wifi.