My grandma has this phone and in her SMS inbox it just has envelope icons without the name of the person who has sent the message, even though they are in her phone book! She has no idea who has sent the text if they do not sign it, which is very upsetting for her.
Hi Carl, checked her phone more thoroughly - turned out that the person who was messaging her had entered her number in her phone again without adding her name to the contact - so there was a duplicate contact! We just couldn't tell because the contact just looked like a space in the contacts list, which wasn't immediately obvious because appeared in a place where you'd expect to see a space! All fixed now, thanks for the tip! :)