+44, drop the leading zero, and know the difference between 01, 02, 03, 07 and 08 before you pick one.
The UK country code is +44. Domestic numbers start with a 0 which is dropped in international form: 020 7946 0000 in London becomes +44 20 7946 0000.
Number lengths vary by area, which is why validation rules written for the US reject perfectly good UK numbers.
The first digits carry meaning, and picking the wrong one sends the wrong signal or costs your caller money.
If you want a national presence without charging your customers to reach you, 03 is almost always the right answer. 0800 is for when you want people to ring you badly enough to pay for it yourself.
And whatever you choose, ring OUT from the same number people ring IN to. A callback from an unrecognised number gets ignored, and that is true in every market we operate in.
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