You seem to be using an iPhone - is your friend using one too?
If so it's almost certainly this iPhone roaming problem due to the stupid way that Apple do things:
You have to be persistent in trying to get that to work.
Switching airplane mode on and then off and then quickly trying it may help to get it working quicker.
As I say this specific problem is down to the stupid way that Apple does things and users of Android or other phones don't have this problem.
Hope this helps.