[emoci]

You would do something like:

If number begins with x


However, it is a bit more intuitive (and easier to deal with) if you just click 'Advanced Settings' and fill things out as follows:

Priority*: You can assign this as you wish (it's really only important once you start setting multiple rules)
Pattern*: _xx.
Comment: This is the place to put any notes for yourself
Replacement*: ${EXTEN}
Provider*: Choose your provider
Active*: Yes
Virtual Toll Free Enabled*: No
ENUM Lookup: No ${EXTEN}
Geographic Lookup: No

Save, then test using the the 'Dial Plan Test' field. You simply enter a number as you would dial it, and make sure VoXalot is applying the correct routing...