By AppleInsider Staff

Published: 11:00 PM EST

Apple on Monday night gave word that it would launch MobileMe just ahead of iPhone 3G, turning on the lights during a six-hour window on Wednesday evening.

A notification sent out to .Mac users warns them that most of the online service's functions will be taken offline between 6 p.m. and 12 a.m. Pacific Time on the 9th, with MobileMe going live "as soon as possible" during this particular timeframe.

"Members will be unable to access www.mac.com or any .Mac services during this time," the notice says, "with the exception of .Mac Mail accessed via a desktop application, iPhone, or iPod touch."

The early handover is considered important both for the widespread adoption of MobileMe as well as the iPhone 2.0 software update, which ties in closely with the new online platform.

Apple hasn't said if or when it will ultimately phase out .Mac permanently, but has so far promised to let users keep at least their @mac.com e-mail addresses and transition over to @me.com only when they're ready to make the change themselves.

MobileMe was announced last month at Apple's annual developers conference as a new Internet service that delivers push email, push contacts and push calendars from the "cloud" to native applications on iPhone, iPod touch, Macs and PCs.

When it launches on Wednesday, the service will completely replace Apple's existing .Mac online services. Existing .Mac members will see their accounts upgraded to MobileMe accounts and new users can subscribe to the service for $99 per year.

MobileMe retail boxes began arriving early on some consumers' doorsteps late last week. A need to know transition guide for existing .Mac members remains available.