Hi ive just done the same my bill was due on the 18th july and now today my bill for this month has come. Ive just paid the bill but after about 6 days after the origional bill my phone was cut off i couldnt make calls or send txts, use the web etc. You can still get incoming calls and msgs though. Hope this helps gud luck xx:smileyhappy:
Its always worthwhile calling Customer Services and speaking to them as they might be able to put a marker on your account that lets them know you will be paying a few days late so you don't lose service.
As mentioned above you do get a few days grace period when you don't pay your bill. Just make sure you call and pay the bill on the data agreed with the Customer Service rep.