Many of us these days have our contacts spread all over the place: Gmail, Yahoo, Hotmail, Exchange, etc. It can be quite a pain.
Starting with Windows Phone 7, Windows Live will take a front and center role with the device, requiring you to use a Live ID to "sign in" on the phone to access your Xbox account, Zune profile, Hotmail/Live Mail, MSN Messenger, Phone Live, etc. This is quite similar to how an Android device requires a Google mail account, which also accesses all of Google's services.
One neat feature that will help simplify things is using Windows Live Contacts(http://contacts.live.com/), which will allow you to import your contacts from
- Microsoft Outlook
- Outlook Express
- Windows Contacts
- Windows Live Hotmail
- Yahoo! Mail (CSV)
- Gmail (CSV)
- AOL Mail
Finally, you can use the Manage --> 'Clean up contacts' option in Windows Live Contacts to find and delete duplicate information, saving a lot of time. Likewise you can use the 'Merge' feature if you have many lists to import.