"If you're switching to Gmail from another email provider, importing contacts and messages from your old email account can help you make the transition without having to do a bunch of housekeeping," explains Google. You can import the contacts from your old account, import the existing messages and the messages you will receive in the next 30 days and create a new label for the imported messages.
Of course, you can also import contacts by first exporting a CSV file from your old account, there's also the powerful mail fetcher that downloads messages from services that support POP3 and you can auto-forward messages to Gmail if your old service has this feature.
The new option should be added to the new Accounts and Import tab from Gmail's settings page.
If it's not there yet, then you'll have to wait until it's available for everyone. One thing is clear: when this option is available, it will be much easier to migrate from Yahoo Mail and Hotmail to Gmail and that could the increase the adoption of Google's mail service. "Between December 2007 and December 2008, Gmail's number of unique monthly visitors in the United States grew 43%, from 20.8 million to 29.6 million, according to ComScore. Windows Live Hotmail lost 5% of its unique monthly visitors during this period, falling from 45.7 million to 43.5 million," reports InformationWeek.
{ Thanks, Kevin. }