If you are switching ISP, please keep in mind the following 3 easy steps and the switch will be much simpler:
1. Compare: Spend some time comparing ISPs in your area. It is a major decision even though it seems small at first. The reason being that once you sign up for an ISP, you will be with them for a while. So all your legwork upfront will come in handy. It is more important than opening a bank account. You know it is hard to change. Changing ISP is even tougher. The reason is simple, the ISP you choose sort of becomes your 'identity on the internet'. You get email from the ISP; your access to the internet depends on the ISP. Come to think of it a lot rides on choosing the right ISP that suits you. You can check out getanisp.com and www.switchemail.com/pages/CompareISPs.asp for comparison of ISPs.
Just don't look at the price. Make sure you are comfortable with everything they have to offer. Number of email addresses. Virus protection. Spam protection. Anything that is important to you; this is the time to pay attention and ask yourself 'Is this the ISP I would like to be with 5 years from now'. If the answer is not a definite 'yes' then walk away. Look for another ISP.
2. Overlap: Once you have found your ISP that fits your needs, then don't just cancel the old one. Overlap the service. Keep the old one online for at least a month. This will save you a lot of trouble. Paying 2 ISPs for a month is a small price to pay for making sure everything works at the new ISP. Secondly, you have time to get all your people informed about your new email address. Thirdly, you can transfer all your buddy lists and other saved information over. Overlapping will give the breathing room to do it at your pace and not leave anything behind.
3. Forward: After a month or so, when you are comfortable with the new ISP, go ahead and register yourself at Switchemail.com. Now go ahead and close the old ISP. In case anyone sends an email at your OLD ISP and they get a bounce back, they can simply forward the bounce to firstname.lastname@example.org and switchemail.com will forward the email to your new email address. You can do the same too. Any time you get a bounced email, forward to email@example.com and they will search and let you know the person's new email address.