I bought my modem for use with NTL's network quite some time ago, for a £5 saving on the charge of (I believe) £50 a month for 512k.
After some time, this went down to £20 pm, including the £5 discount, while others were paying £25 and NTL gave them a modem.
Following the upgrade to 1Mb, NTL decided to drop the discount for owners of modems, and so i have been paying the same as someone who didnt have their own modem, and was given one by NTL.
This has never been an issue till the 10 meg upgrade, where my modem is, I believe, somewhat lacking since it is rather old.
Hope thats cleared it up