Abbreviation for "telephone number"

Is there any way of abbreviating the term "telephone number" which is recognised as more correct in British English than other ways?

I've seen "Phone 12345", "Phone: 12345", "Tel. 12345", Tel.: 12345" and others, and am wondering which one to choose for letterheads.

Also, are country code, area code and own number just separated by a space, or would it be more correct to put a hyphen or slash in between?

Thanks!

Thanks, Feebs!

I suppose when using the same letterhead for international correspondence a lot, this would also be fine?

Tel.: ++44 (0)111 2222222

In Germany, I'm just used to putting two plus signs to denote that whichever two digits precede the country code in the country a person is calling from, should be added here. E.g., when calling abroad from Germany and most other countries I'm aware of, one would use 0044, but from South Africa it would be 0944.

Is it something which is not being done in English?

Thanks, Englishuser - obviously, my reply hasn't come through yet.

Would you put +44 (0)111 2222222 then?