Sometimes my daughter sends a text to our landline I'm sure it comes up as am 0845 number, you just have to follow the instructions, the message will say that it is a text message from BT (pretty certain it ends with a lot of 1's)
I looked on Google. Some say its safe its a BT number but it was asking for my mobile number? Its been used since at least 2007 according to what I read.
Anyone who has my number are friends. No one will get it from me other than who I choose.