asterisk users - Sep 2005 - voicemail context. macro, and directory

I use a macro to dial most of my extensions and in the macro the
variable ${macro_exten} is used to send calls to the right voicemail
box.

I also use realtime MySQL for SIP, voicemail, and extensions.

When I put a voicemail box in a voicemail context other than default the
method of getting the caller to voicemail fails as it does not include
the context.

Is there a built in channel variable that I could read to get the
'mailbox' field from realtime sip? If so I could then store the mailbox
value with the context attached, like 5555551212@context.

Not sure how MySQL will handle the @, but I assume that since it is in a
text string it should be fine.

If there is no existing variable I guess I could read the entire row
from the sip table to the macro with realtime()