Apple has sent a note to Genius Bar employees alerting them to low stock of the iPhone 3GS and advising them to give customers an iPhone 4 in the event of a swap repair.

9To5Mac published the note, which was sent to Genius Bars worldwide, on Saturday. The note tells employees that, “until further notice,” Genius Bars should first perform display repairs for the iPhone 3GS, then discuss the advantages of buying a new iPhone if the 3GS is almost beyond repair, and finally, in the case of a swap repair, use on hand inventory.

“When there is no iPhone 3GS stock on hand for a swap repair, MobileGenius will offer an iPhone 4 as the substitute part. Customers will need to go to their carrier for a micro-SIM to use with the iPhone 4,” the note reads.

The shortage of iPhone 3GS stock suggests that Apple will be discontinuing the older model when the iPhone 5 is unveiled, which is expected to be at a 12 September special event.

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