According to Tmo News, which calls itself the unofficial T-Mobile blog, T-Mobile is planning to schedule employee blackout between September 20 and September 22. This essentially means that T-Mobile employees will not be able to take a leave for the purpose of a vacation during this period. While it's not directly related to the iPhone's release, carriers do institute blackout periods for busy days which also includes days just immediately after the release of a new iPhone.
If one connects the dots, Nikkei, the Japanese business publication had earlier suggested that Apple would release the iPhone 5S and the low cost iPhone or iPhone 5C on September 20 in Japan, indicating that the first wave of the new iPhone's release would commence on the same day. Greece-based website, Techmaniacs had also confirmed that the iPhone 5S and the iPhone 5C would launch on September 20
A number of rumours including some by credible publications and journalists have confirmed September 10 as the most probable date for Apple hosting a special event to announce the new iPhone(s).
The iPhone is usually made available to the public in major markets including US, Canada, France, Japan, Hong Kong, UK, and Singapore, around a week after the official announcement.
Apple has not sent any invitations or announced an event officially, yet, though it typically sends out official invitations only a week before the actual event.
The iPhone 5S is expected to come with a brand new Apple chip, the A7, alongside 1GB of LPDDR3 RAM, retaining the form factor of the iPhone 5. A 128GB storage variant of the phone has also been rumoured. The iPhone 5S is likely to come with a larger f2.0 aperture compared to the iPhone 5, that comes with f2.4 aperture. It's also likely to sport a fingerprint reader.The low-cost iPhone or iPhone 5C has leaked several times. Alleged pictures of the iPhone 5C have revealed a plastic polycarbonate body back panel in White, Blue, Red, Yellow and Green colours, a round camera lens and LED flash, Apple logo and iPhone branding. It's expected to be powered by a dual-core CPU, and have a 4-inch screen, just like the iPhone 5, with a resolution of 640x1136 pixels. The iPhone 5C is rumoured to have 1GB of RAM, and come in 16GB, 32GB and 64GB storage variants. It'a also likely to sport an 8-megapixel rear camera and a 1.2-megapixel front facing camera camera and run iOS 7 complete with Siri which would be available in English, French, German, Japanese, Chinese, Korean, Italian and Spanish.