The default sms inbox in WM 6.x is threaded. Similiar with PALM. Some luv it some don’t. For me its annoying. Heres the solution, you need regedit software first.

create a folder named OEM in HKEY_CURRENT_USER\Software\M!cro$oft\Inbox\Settings

Then in the new named OEM folder, create a DWORD key called

SMSInboxThreadingDisabled

with a value of 1

Tested and working in my prophet. Careful, do it on your own risk
taken from xda-forum by ziadah