[cisco-voip] Route pattern prefixing a "+"

[IT]

I am using Level3 as a SIP trunk provider (through Bandwidth.com), and
they are using the numbering format of +1XXX-YYY-ZZZZ. The issue I am
encountering is with the "+".
This is not a problem for incoming calls, as I setup the trunk for only
10 significant digits. However, when I try to use the trunk for outbound
calls, I get the SIP error that my number is not formatted correctly.
The issue is that I cannot prefix a "+" to the beginning of the route
pattern. I have tried adding the "+" in the route pattern configuration
but CCM tells me that the + is not a valid digit. How can I add a "+" to
the route pattern?

Thanks,
Avidan