when i searched for answering service i found this one for $8.95 per month. not sure where you are...http://www.voicenation.com/
and here is the musicians answering service in london
http://www.maslink.co.uk/
if you intend to hold youjr evbent in the same venue each time
perhaps the venue would be willing to field calls..
or have an extension for you....i have called osme people's
houses wher ethe ansent machine says if you want to leave a message
for Mr. X push 1, for MS. X push 2, for little X push 3..
that might be a function of the answering machine you have.