everyone with the problem of not being able to find the correct key to copy and paste, i had the same problem. the reason why you can't find it, is because it's not there. some apps modify the registry. in my case it was textr. i tried it before coming upon this thread. even after uninstalling textr, the registry stays modified and the needed key is missing. i had to hard reset my i760 to get it back. i know that some of you tried hard resetting to no avail, so i'll outline exactly what i did step by step, just in case the order of actions has anything to do with it. so:

1. hard reset the phone (hold down the middle enter button and hit the reset switch - you should see "clearing data" on the screen)
2. send an sms and mms to yourself to make sure the service works and it's not a verizon problem.
3. install resco explorer and registry plugin cab files (since you'll need them for this operation)
4. clear out your sms and mms messages to eliminate conflicts later
5. open task manager and close all running tasks
6. install the threaded sms plugin
7. open resco and do the registry mods:

a. Using a registry editor app, navigate to HKEY_LOCAL_MACHINE\Security\PushRouter\Registrations\ByGenericId
b. Delete the PC10 key (folder).
c. Find the key that has a 'Path' value of "\windows\MMSBallon.exe" and copy the 'GenId' data value. It should look similar but not identical to 80409F46E414C801 (this should be the first key in the ByGenericId folder).
d. Navigate to HKEY_LOCAL_MACHINE\Security\PushRouter\Registrations\ByCTAndAppId\application/vnd.wap.mms-message\Default
e. Change the Default data value to the GenId from step 5.
Navigate to
f. HKEY_LOCAL_MACHINE\SOFTWARE\Palm\Varnish\Messaging\
g. Delete the MMS key (folder)
h. Soft reset.