scam?

I will be turning my mobile off at night, which I dont like doing, as my family might be trying to get in touch. Probably best to set it to silent. Then I am in danger of forgetting and missing calls.

All sounds very odd, I would treat it as scam. If it is genuine, they will contact you again.
It is correct that you are allocated a temporary number during a phone change over, I had exactly that, but no one saw that number.

Looks like it is a scam as others have received similar messages on this old forum thread - goo.gl/tHfN5L
Seems odd that they had your friend's number though.
I would add the number to my reject list and forget about it.

Why send a text saying do not want to disturb at 5am. Cos they know you are likely to contact them back. Do not contact the senders number. I Fear it is a scam. If it's a real concern they would have sent a message.
Really the scam world is getting to much.