or use the IP-Office Manager populate the 'DTMF Breakout' numbers for the mailbox. Then let the mailbox owner provide the details.
or (assuming Intuity mode)
While initial prompt is playing Press '*8'
or '#' and details get provided.
If leaving a message, press '#' when finished, '#' to send,
then press '*8'.
*8 will then allow another number to be entered.