You cannot go over as data just stops once you reach your allowance. You then have a choice of buying a data bolt on or waiting until your allowance resets on your billing date.
Also can you keep your same number? Ty!
Yes you can
The upfront fee might vary each year but yes you'll need to pay something I would imagine.
It comes off the total price for the handset though.
Track usage, upgrade and get support with the My O2 appDownload My O2