3 Mobile Broadband

Ive just signed up to a 24 month contract with 3 Mobile and just got a letter saying my allowance is 5GB(so every month you could send 3250 emails and surf the internet for 150 hours, as well as download 150 - 2 minute videos and download 300 music tracks)

Im paying £30 a moth for a laptop and LIMITED internet.

Is the 150 hours internet a guideline or will they disconnect it if I go over?

Thanks for your help in advance.