If you really think the problem is the handset, turn on sip debugging on your cucm. Make the same call. Then check the logs to see what cucm thinks your phone is sending. Assuming it sees the phone sending *1, you can write off the problem being on your phone.

Also, if you think the problem is your phone, you could always update the firmware. You'll have to do this from you CUCM. But again, I strongly believe the problem has nothing to do with the handset.

An even simpler test is to try your same call from a different type of phone in your office. It should go out the same PSTN access point as the 9971. If that does work, then you could be on to something. If it doesnt, you know the problem is further up the chain.