It is that time of year again when iPhone rumors ramp up more than usual. All year long we hear about the next iPhone and what it may contain but it is around now that things kick into high gear. Speculation has been high about the iPhone coming to Verizon and AT&T getting a new version.

We may now have the strongest piece of evidence that a new phone is due this summer though. Each year since its inception, the iPhone has been announced at the Worldwide Developers’ Conference and been released shortly thereafter. The phone is due for a refresh.

In a turn of events, it is now being reported that AT&T has restricted employee vacation in the month of June. The only time this has happened in the past was for previous iPhones and not it is happening again. The timing could be coincidental but what could be the reason if not another iPhone.

The next phone is rumored to have a better camera, possibly a front-facing camera, the Apple A4 silicon chip, more memory, better battery life, and even a touch based case (like the magic mouse).

All of this information in concert with the definitive release of the next iPhone OS (version 4) makes for a pretty substantial rumor. We have seen minor releases of the OS throughout the year on existing models but  major releases have traditionally arrived on new hardware. To that end, OS 4 will not be compatible with the original iPhone 2G and only portions of it will be available on the iPhone 3G. It stands to reason that the 3G S and the forthcoming next-generation device will be Apple’s two devices.

Time will tell but June is not far away so you don’t have to wait long.