After emailing Voipo support, I did get an answer on this. Basically, I was told that the star commands for the pap2t will be the same as those for the GrandStream, but the are all still in beta. From another thread, the commands listed were:
*20 [phone_number] - Call Forward
*21 - Call Forward Disable
*22 - DND Busy
*23 - DND - Voicemail
*24 - DND Disable
*25 [phone_number] - Set Failover Number
*26 - Set Failover to Voicemail
*69 - Return Last Call
*27 - Add Last Caller to Blacklist
*67 - Block Caller ID (Single Call)
*30 - Block Caller ID (All Calls)
*31 - Unblock Caller ID (All Calls)
*82 [phone number] - Send Caller ID (Single Call)

RA