I was able to txt my father in law a couple of weeks ago, Vodafone to Vodafone, but since then text messages don't arrive. I can call him, he can txt me, but I can't txt him.

It's not important enough for me to call Vodafone and talk to first level customer support. If I provide time and phone number details is anyone able to check if the system thinks the messages were delivered? He uses a very simple phone, I don't see any blocking or anything on it.