The mobile mast shouldn't have a significant affect on broadband or wifi, your own mobile signal will be a lot stronger due to its proximity.
If your (home telephone) cabinet is fairly close I'd seriously look at spending the extra bit of money on fibre, it removes all the uncertainty of the signal from the exchange to the cabinet.
The only thing you have to remember with most non-virgin fibre is to never switch the router off for less than half an hour, its actually an openreach thing which talktalk has no control over but are doing an upgrade sometime in the future. If its switched off for less than half an hour, the wizadry assumes its a dodgy signal and reduces the speed, over half an hour and it does a reset and tries for maximum speed.
In a time of universal deceit - telling the truth is a revolutionary act. George Orwell
When the debate is lost, slander becomes the tool of the loser. Socrates