No other parents I know of let their kids have their own mobile phone at that age and it had been our established policy too.
However, W gave one a mobile phone to keep secret from me and to secretly use it to contact her. Kid was distraught at being put in that position by W. I thanked the kids for telling me and I said there was no need to keep it a secret.
I showed them how to use it. They had no interest at all in calling their Mum or anyone else. They only used it for text messages. I had it in between times to charge it up for them and so they didn't use it during meal times, at school (where kids phones are banned), during homework or bedtime. They don't call W and she accuses me of being controlling. One said they missed W so I suggested they called her. I didn't speak to W then or the next day when she called the main house phone to speak to them in the morning before school. I just answered and gave the phone to the kids.
I wondered whether giving-in over the kids having a mobile phone (W has got her own way over that) and encouraging the kids to contact their mum would be seen as W cake eating?