Due to low stock of the iPhone 3GS, Apple Genius Bar employees will now be offering reduced service options for the old model and instead making a hard pitch for the new iPhone, which is expected to be announced at an upcoming launch event later in September.

Our pals over at 9to5mac were sent an internal memo to Apple Genius Bar staffers stating that as of now, “The service options for the iPhone 3GS are: perform display repairs, discuss advantages of buying a new iPhone … use on-hand inventory for swaps.”

The emailed memo goes on to say that if the store in question is out of 3GS units, the customer will be offered an iPhone 4 as a replacement. All this points to a possible discontinuation of the 3GS, although units still in circulation will still have software support — for now, at least.

The Apple rumor mill has been buzzing lately with questionably accurate data points about the iPhone 5, but we do know that Apple has at least one big announcement event coming up this month. At that event, Apple may make some statements and show off some units to announce the iPhone 5 and/or the iPad mini, another rumor-laden mystery that may or may not be verified by Apple in the coming weeks.

In a sign of things to come, Verizon has blacked out the last week of September as no-vacation days for employees; AT&T did the same.

For your convenience, here’s a roundup of all the rumors to date and a handy diagram of leaked hardware parts and specs.