Intercepting Outgoing SMS Messages

[TimY]

We have a requirement on the project I'm working on to filter (and
potentially redirect) outgoing SMS text messages after they are composed in
the native Windows Mobile text messaging application. The most reliable
approach would seem to be replacement of the default SMS transport with my
own version, by using a COM component that implements the IMailSyncHandler
interface and registering the transport (the Transportdemo sample was used as
a basis for my test component). That would give me the ability to inspect
and act on outgoing SMS messages.

I've tried installing and registering my homegrown custom SMS Transport, but
have been unable to replace the default transport that lives in tpcutil.dll.
I know my transport component works, as I have successfully registered it as
a new custom transport. It seems like the
HKLM\Software\Microsoft\Inbox\Svc\SMS key DLL string value that specifies the
DLL that implements the transport is being ignored. I've tried soft
resetting the device after making the registry change, but it's still no go.

Has anyone tried or been successful in replacing the SMS transport using
this technique?

TIA,

- Tim