Hi!
I see that @jfinstrom committed something which seems to be related to this for the FreePBX 13 Beta but it unfortunately didn't work for me (if the intent was to fix this problem).
re: http://git.freepbx.org/projects/FREEPBX/repos/core/commits/a9852e703c445135ab4e3f76bda7f6d733d63b43
and
Executing [1235551212@from-trunk:9] Set("SIP/Voipms-00000002", "_REVERSALREJECT=FALSE") in new stack
[2015-09-08 19:34:42] WARNING[8049][C-00000536]: func_channel.c:596 func_channel_read: Unknown or unavailable item requested: 'reversecharge'
It realllllllly looks like Asterisk doesn't do lazy evaluation so "${CHANNEL(reversecharge)}"="1" should not be on the right side of the "&" if it is not available for that channel type..
Have a nice day!
Nick