Rumors are in that Apple retail stores have already received shipments of unidentified boxes believed to contain 3G iPhones.

This starts to become a complete tracking of the path the 3G iPhones are taking. It started with ship containers, over to warehouses and now the last stop before it will be in your hands.
Arstechnica is the source for this rumor. They also claim that Apple stores have received a new signage that goes up on Monday.

Slightly more mysterious is a related additional rumor tidbit. The London Regent Street Apple Store has received a single box that is padlocked, and under orders to be put in a safe until Monday.
More details on Arstechnica.

This lets us believe that the new iPhone is not only going to be announced on Monday, but that it also is already in Apple stores on Monday. Start to line-up now.
More 3G iPhone News.