DNID sometimes contains the number that was dialed.

From asterisk-1.4.20.1.tar.gz; docs/channelvariables.txt:
${DNID} - Dialed Number Identifier (Deprecated; use ${CALLERID(dnid)})

Asterisk implementation comment:
I do not know when it works or not nor when it is supposed to work or not.
See http://bugs.digium.com/view.php?id=2590

See also

• RDNIS
• DNIS