Thank you for your post and welcome to the forums.
I'm sorry to hear you're faced with this issue, let's get the ball rolling and see if we can resolve this. Firstly, it would be great if you could let me know if this is still an issue? Moving on from that if It's not the case, can you expand a little more as to what is going on? The numbers yo are trying to message, are these select few, same network etc? What happens or what error do you get when they don't send?
HI Mumoftheyear, thanks for the reply, how are the numbers saved in the phone is this 07 or +44, does changing the way they are saved help at all? Do they have any issues when texting or just you. Is there a particular network which you cannot text? Chris
I had this problem using an android phone on O2 a few years ago. I could call people but not send texts to them unless they had texted me, and even then not always. If we used What'sapp it worked ok.
Tested (in a pub sat next to each other, so we could drown our sorrows if it didn't work) by removing her contact details and then re-adding that number and everything then worked for that contact, so did the same with all contacts.
Time consuming but it worked for me.
I can't remember whether they were saved to my phone or sim though.
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali