How to call telephone number through asterisk trunk from external application talking through prophecy?

Question

Wow, that title was a mouthful...

I'm sure that sounds very confusing at first glance. This is the basis of what I've got going on:

I have:
-a server set up with Asterisk and Voxeo Prophecy running on it.
-Prophecy set up as extension for Asterisk.
-another server running an external application.

The external application generates some two XMLs: one ccxml and one vxml file, for Voxeo to read and execute, which then initiates a call to (up until today) an asterisk extension.

The project is moving along, though, and yesterday I got a SIP Trunk and a DID number in hopes to turn this application into something that can call real people.

The trunk is working on Asterisk, and I've been able to initiate calls through a softphone (X-lite) to my cell phone number. That works just fine.

However, when I try to initiate calls from the external application, it does not go through. I've tried numerous things to try to fix it but it's just not working.

Prior to the trunk/DID business, the working code to call an asterisk extension was as follows:

 <createcall>dest="'sip:*Extension here*@*IP Address here*'" 
 connectionid="myOutBoundConnectionID" timeout="'45s'" callerid="'*Extension here*
 @*IP Address here*'"</createcall>

My first thought was that I might need to have a trunk specified for Prophecy as well as for Asterisk, but I'm probably way off base.

The reformatted code that I thought would work was as follows:

<createcall>dest="'tel:*Phone Number here*'" connectionid=
"myOutBoundConnectionID" timeout="'45s'" callerid="'*Phone Number here*
'"</createcall>

...but this does not work at all.

The log files say things like this when I call from my softphone:

-- Executing [*My phone number*@from-internal:1] Macro("SIP/1001-0000007d", "user-
callerid,LIMIT,") in new stack

but when I call from the external application, things are a little different:

-- Executing [*My phone number*@from-sip-external:1] NoOp("SIP/*IP Address:5080-0000007c", 
"Received incoming SIP connection from unknown peer to *phone number*") in new stack

Can anyone shed some light on what is happening here? Thanks in advance!