ISP is set to an address. It can't be used elsewhere.
You can use someone elses ISP using their modem and login details.
You might be albe to logon wirelessly to their setup if they use a wireless router. Or network cable thru their PC or router.
Some hotels, Pubs, Cafe have WiFi spots you can use.
http://www.thecloud.net/content.asp?section=4&content=39
You can buy a data card which goes into your laptop and uses a mobile type sim card, not cheap to run.
http://www.vodafonebusinessshop.co.uk/index.cfm?fuseaction=MobileEmailAndData.dataWelcome&WT.srch=1
If your buying a new Laptop read my PC help site webpage on security. What you need, Why you need it, Where to get it, All free. Download it now to CD so you laptop it secure before you hook it up to the internet
http://www.phpbbserver.com/stevie19605/viewtopic.php?t=40&mforum=stevie19605