As of Asterisk 1.8 a prefix is no longer valid for choosing the busy / unavailable announcement:
VoiceMail(u${ARG1})
You need to pass it in the options instead:
VoiceMail(${ARG1},u)
As of Asterisk 1.8 a prefix is no longer valid for choosing the busy / unavailable announcement:
VoiceMail(u${ARG1})
You need to pass it in the options instead:
VoiceMail(${ARG1},u)