BST
Yes I did realise you want to use the laptop when away from home, and it can be done except that the ISPs that I have done it with require the ADSL service to be inactive for it to work.
Presumably the key will be finding one that will allow dial-in (into the same ADSL account) while your home ADSL is active.
If you are the only person at home using ADSL, just switch off your ADSL modem on your way out, and then you can do this with many ISPs.