Apparently, for some older Windows Phone 7 devices, especially on Sprint, there are certain limitations on SMS and MMS. To be limited to the standard 160 characters in SMS is not fun, especially when trying to get a full thought in before someone texts you back. MMS limitations have never popular either. While most devices on most operating systems can bypass the 160 text limit rather easily, the MMS limit is usually boosted as high as possible, but there’s still a limit.
For those on the HTC Arrive, you can now have unlimited SMS characters and essentially unlimited MMS size thanks to XDA Senior Member mapaz04. This will most likely also work on other Windows Phone 7 devices, but it untested at the current time. The mods require different methods to implement, but neither is very complicated. For the SMS to go above 160 characters, users simply need to change a value from 0 to 1. Says mapaz04:
1.) Go to HKLM\Comm\Cellular\SMS\Router\CDMA and change the Contantenation entry from a 0 to a 1
2.) *** Very important thing (as of now)*** Select the EXIT from the Registry Editor (DO NOT BACK OUT of the app, press MENU then EXIT)
Then test to be sure it worked. Nothing too hard.
For the MMS it’s much the same process but a different value.