Windows Phone 8 (codenamed Apollo) is the next major version of Windows Phone and is expected at the latter half of 2012. It will follow Windows Phone Tango (7.6) and Windows Phone Mango (7.5).It has been assumed that Windows Phone 8 will borrow some parts of the Windows 8 kernel and thus be incompatible with the current generation Windows Phone apps.
This rumour was sparked by a recent tweet by tech blogger Eldar Murtazin who had the following to say:
"WP8 os isnt compatible with wp7 on app level (u need to rewrite all apps). Thats another os core with metro ui".Brandon Watson, Director of Developer Experience responded on Twitter with the following clarification:
"...Any app built today will run on next major Windows Phone version".So this should clarify the question of current generation Windows Phone apps being compatible with the next version of Windows Phone. But Microsoft eventually plans to bring a common Windows operating system to all platforms and we will face this issue sometime in the future.