When writing up bug reports for this column, I prefer to have guaranteed solutions to offer. However, a few problems are so frustrating and mysterious that I'll cover them even without a known reliable fix. That's the situation today.
A few weeks ago, I sent several SMS text messages to a friend via the Messages app on my iPhone 5. They went unanswered. I eventually learned that he had never received the messages. Not only that, he had sent me a couple of messages during the same time period that I never received. When we finally sat down together to figure out what was going on, we confirmed the obvious: we could neither send nor receive text messages between our two smartphones.
Here's where things gets weirder. My friend is the only person I cannot text. Ditto in reverse for my friend. Not only that, we have been exchanging texts for years without any difficulty. It's only in the past few weeks that we've had this difficulty. He is using the same smartphone (not an iPhone) and same carrier he's had for the past two years. The only apparent change that might be linked to when the symptom first popped up was on my end: I upgraded to an iPhone 5 and iOS 6 around the time the texts started to fail (although I can't confirm that the failures began immediately after the upgrade).
I tried a couple of obvious potential fixes. First, I restarted my iPhone. Second, I deleted the entire conversation with my friend and began a new one. Neither had any effect.
Next, I searched the web for reports of this same bug--hopefully from users who had better luck in finding a cure. A bit to my surprise, I found numerous blog and forum postings describing nearly my exact situation: texting failing with only one person. The occurrences spanned different smartphones and different carriers.
Various solutions were offered. All of the ones cited here were successful for at least one person.
A user in a MacRumors posting had the texting problem only when using iMessage, not SMS. This was not the case for me.
A person in an Apple Support Communities posting had the texting failure on an iPhone 4S running iOS 5.1.1. He found that upgrading to iOS 6 eliminated the symptom. As I was already running iOS 6, this did not seem promising for my situation. I suppose I could do a restore of my iPhone, to reinstall the current iOS version, but I haven't yet been willing to go that far on what is likely to be a dead-end.
A Verizon thread suggested deleting both the the conversation and the contact entry for the person you cannot text. Next, text using the person's numeric phone number, rather than their contact name. I tried this; again to no avail.
A second Apple Support Communities thread offered a variation on the Verizon tip. It involved going to Contacts and temporarily altering the phone number of the friend. This allows you to enter the person's phone number in Messages without the app linking to the Contacts entry. However, the thread also referred to international dialing codes, which were not relevant to my situation.
A thread at the everythingiCafe advised sending texts as "group text" (using the person's name/number twice). This worked in a couple of cases, although no one seemed to know exactly why.
As you can probably surmise by this point, none of the above suggestions worked for me. A precise cause and cure remain elusive. I still cannot send text messages to or receive messages from this one particular friend. For now, we've had to use email as a fallback. Texting with everyone else continues to work just fine for both of us.