Q: Why can't I dial my mobile number 078137xxxx. When I call this number from my computer it does not ring. I am told there is no one available to take the call.

A: This number does not exist "07813791888"

There is no country code "078". The proper way to dial a number is country code + area code + number. In general, you do not have to dial 00 or 011 or any other prefix before the country code when dialing any number.

One exception in dialing instructions is when using Ekiga.