Wow, you do text your Mum a lot.
If you've been with Orange and you move to O2, you'll never leave O2 again. They're totally awesome. Best signal, best customer service, best prices. Don't know how Orange keep going as I've found they're the worst for everything. 2000 would quite easily be covered. I'd have thought you'd need to get upto about 8-10,000 to be in trouble. I've sent over 2000 a month before and not had a problem. Some people send texts using Nokia PC suite so they must send loadsssss.