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Not directly. However, you can hairpin the backup PRI to the PBX through another T1 port on the TA908 (configure it for role user and be mindful of clocking) and then build a voice grouped-trunk out that trunk with a higher cost than SIP. The PBX will send the calls to the TA908 which will try SIP first, then use the PRI after a brief post-dial delay. You'll likely want 9-1-1 to prefer the PRI as well as possibly other service codes that are handled locally like Dig-Alert, 3-1-1, etc.
What is the TDM connection? PRI, RBS, or FXS?
If PRI, you could busy out the PRI trunk using Network Monitor. Here is config guide: Configuring Network Monitor in AOS
Here is an example of setting up a ping probe on the sip server. If the wan goes down, it will busy out the PRI trunk. You apply the track under the PRI voice trunk as shown in config.
probe FAILOVER icmp-echo
destination <IP of SIP Server or Internet address that replies to pings>
tolerance consecutive fail 5 pass 2
snmp trap state-change
test if probe FAILOVER
voice trunk T02 type isdn
description "PRI Trunk"
busy-out monitor track WANTRACK
Let me know if you have questions.