For the past few years Apple have released each iPhone in September.. Generally on a Friday, and around the 21st or 22nd.
As there’s currently nothing to suggest this news has actually leaked, it’s believed the German carrier may well just be guessing, based on previous release dates.
As the WWDC is suggested to be the event at which both the 4.7 inch iPhone 6 Air and 5.5 inch iPhone 6 Pro (dubbed by the media) unveiling, it’s not clear if they are both going to released together. Or on separate days.