My DD13 got a phone when she was 12. We allowed limited texting. She got 400 messages a month.
We initially shared the OP's belief that it wasn't really necessary, but have discovered there are times when it is VERY convenient. We don't read her texts but know that most of them are either simple chat, or actual necessary information (such as "we're on our way to pick you up - be waiting outside in 3 mins").
She has been very responsible with her texting (not exceeding her limit) so for her 13th birthday, she got unlimited texting. It's on all our phones now, and is actually cheaper for us to all have unlimited, than to have the 400/month package for each phone. I'm still not very good at it, but I'm learning. I like doing things like sending a simple text to multiple contacts instead of having to make several phone calls. For example, if I'm traveling, I can text "arrived safely" to everyone who would care, and I'm done, instead of calling my DH, parents, etc. when I land. It's also nice to get a quick text when you're in a situation where talking on the phone would be inappropriate but you need to communicate.
DD homeschools, so using the phone at school is not an issue, but she does get dropped off many places, so the phone has been very handy. There isn't a phone accessible to her in the building where she takes ballet, or ballroom dance, nor at the barn where she takes riding lessons. She also goes to many youth functions with the church. Many of these are Christian concerts in outdoor ampitheathers (no phone). It's likely the adult in charge has one, but if they get out early/run late, and EVERY kid had to borrow the teacher's phone to contact a parent, it would take too long. It's good for her to have her own.
DD10 is now begging for a phone and has been for over a year. There is no NEED for her to have one (she is not dropped off anywhere yet), however, to kids now it isn't just a utility like a phone is to DH and I. We didn't bat an eye at buying her a Nintendo DSi, and it's way more expensive than a phone (even including the annual cost of another line!) and it can connect to the internet, while any phone she got would not do that. (we only get the free phones - lol) So, we're having a hard time coming up with a reason for her not to have one, other than she doesn't NEED it. Of course, the reason that we say no is good enough, but she has now saved up enough to pay for an entire year of service, so she wants to know why, if she is allowed to buy other things she wants with her money (she did pay for half her DSi), why not a phone?
So we are thinking about it.
If she gets a phone, I have no problem with her texting, but she will not be allowed to take her phone to school (she attends public school).