According to Verge editor Tom Warren the next version of Windows Phone 8, GDR3, is currently in testing.
The software update is rumoured to support 1080P screens and quad-core processors, needed to support the current high end standard for smartphones.
Nokia is said to be in advanced developer of a phablet using the same hardware and software, with the device expected to be released later this year. HTC is also said to be working on a Windows Phone version of the HTC One with similar specs.