Here’s a tricky situation that threw one of our clients for a loop recently. Texts they sent in Messages via iMessage (indicated by blue talk bubbles) to their assistant, letting her know they were stuck in a meeting weren’t being delivered, leaving their next appointment wondering where they are . But other texts were working just fine. The issue, it turned out, was that Cellular Data had somehow gotten turned off in Settings > Cellular. So everything worked fine as long as the iPhone was on Wi-Fi at home, but as soon as they were on the road using a cellular connection, the iPhone could no longer communicate with the Internet. In theory, Messages should fall back to SMS (indicated by green bubbles), which doesn’t require cellular data, but that doesn’t always happen. The fix? Just enable Settings > Cellular > Cellular Data again.