I have been using a Gmail account for a number of years, and as stated, moving ISP is no issue at all with a Gmail account, travel anywhere in the world - log on and away you go. BUT, the best thing about Gmail is..... using it with an Android phone. The SYNC function is sooooo good.
I use the Gmail contacts section for email and phone contacts, Change or add a contact and within seconds your phone updates the new info. Lose your phone ?, get a new phone ? - no problem, simply get new phone, add Gmail account and set it to sync. All your old contacts will appear in the new phone almost immediately.
For convenience, my wife and Sync to the same list. Another advantage is maintaining your contact on a BIG computer screen, not a small phone screen.
I know lots of our members would be using sync, but for those not syncing Gmail contacts to Android it will be a revelation in my opinion. Sync appears on other systems, but I am only familiar on the Gmail/Android version.
Cheers
Alan