Dealing with Area Codes in Phone Number fields

Ok so I know a similar(ish) question has been asked before re: friendly format for Phone Numbers.

My question however focuses on a more specific part of this question, namely the 'dropped' first zero issue in the city code.

I am looking at redesigning a web form where the user currently enters his/her phone and am attempting to make the whole city/local code issues less ambiguous.

I have included some samples in the attached image.

Option A is as the form currently stands. In this case the user (assuming from London) could enter a many variants on the city code. I know I sometimes stop and think when I get to this point in at a form 'What is the most appropriate format'?

do I enter the zero or not, so I enter plus sign, brackets, hyphens or any other characters etc..

Option B - has a note underneath the field which displays to the user the preferred format to enter.

Option C pre-empts the city code and enters the initial 0 for the user, so 207 could be entered here.

Option D - a dynamic drop down who's contents change depending on the option the user chooses in the first(country) drop down.

What do you guys think about this? There is an element of guidance/information I like about option C although maybe it is still a little ambiguous in it's own way. Option D I feel simply may not be doable for various reasons.

Or if anyone knows of anyone has any other ideas or knows of any existing patterns that handle this issue well, I would be interested to discuss them here.