I want to increase voicemail message limit

In file /etc/asterisk/voicemail.conf change value maxmsg

Description of this value: This limits the number of messages in a voicemail folder. The maximum value is 9999 (hard coded) and the default 100. When a mailbox has more than this number of messages in it, new messages can not be recorded and vm-mailboxfull is played to the caller. No more messages possible is also logged

Reload asterisk after that.

See also

• http://www.voip-info.org/wiki/view/Asterisk+config+voicemail.conf