A
As VidJunky said. And set your text app to not send group messages, but to send individual texts to each recipient. (Unless you pay for each text, which is almost unheard of these days.) Because a group text is sent as an MMS, and they can fail a lot more easily than an SMS can. As long as you have unlimited texting, it's no difference to you - it saves a little bit of space on the carrier's MMS server - and if one fails, just that one fails, it doesn't cascade and fail for the rest of the group.