When it comes to iPhone 5 rumors, they seem to fall into three categories. First, release date. The latest in that department put the launch in early October. Second, specifications. Recent rumors suggest the new device might be thinner and wider than its predecessors.

Lastly, carrier rumors. The biggest one of this season is that Sprint will be getting the iPhone 5 whenever it finally launches.

This rumor falls into the latter category. According to a source quoted by Beatweek, Sprint is busy installing network repeaters in Apple retail stores. It looks like they might be gearing up for an imminent launch.

Now there’s evidence that Apple is beefing up Sprint signal quality at its own stores so that would-be iPhone 5 buyers will be able to put the device through its paces on the Sprint network in quantity while still in the store.

According to the source (a resident of Austin, Texas), “One thing I can tell you is that the electrical contractor that I work for is contracted to install Sprint ‘repeaters’ at The Domain. There is a Apple Store at The Domain. One of the ‘repeaters’ is to be installed INSIDE the Apple Store. There is to be a total of 5 ‘repeaters.’”

This rumor adds more fuel to the “Sprint iPhone 5″ fire, as it is one of a few substantial hints at the upcoming release that we’ve seen in the last couple of weeks.

Near the end of August, the WSJ cited sources who said Sprint will definitely start selling the iPhone 5 sometime in the middle of October.

About a week later, an internal memo surfaced from top management asking employees at Sprint dealers to “not speculate about sprint getting the iPhone 5.” The memo told employees that they should respond to customer questions about the new device with a “no comment.”

And yesterday, a leaked document from Best Buy surfaced showing that they expect the iPhone 5 to launch on Sprint during the first week of October.

Sprint would be the last piece of the carrier puzzle for Apple. If the iPhone 5 launches on Sprint, that means that the device will be available with all three top carriers.