Apple will introduce its MobileMe this week in preparation for the release of the iPhone 3G on July 11.
A note on the .Mac pages warns existing subscirbers should expect to lose access to their account, with the exception of dektop-based email access.
"As part of the MobileMe launch, www.mac.com will be taken offline at 6pm PT on Wednesday, July 9th," Apple warns. "Members will be unable to access www.mac.com or any .Mac services during this time with the exception of .Mac Mail accessed via a desktop application, iPhone, or iPod touch.
MobileMe will be available as soon as possible during this maintenance window."
The new service will offer email, calendar, AddressBook, image gallery and storage capabilities as well as "Push" mail and sync services.
Existing .Mac subscribers should already be able to send and receive emails at their new @me.com addresses.