We have had several reports of low outbound volume on Allworx 12 and 24 button phones. This has been on analog and PRI interface. We're not sure yet if its on SIP trunks or not.
Is anyone aware of this problem?

Yes.

I have 2 client that complain of the same issue. One has Cox analog service and another on Qwest dynamic T1; a 6x and 24x...

Never had an issue. What software version are you running?

We have had some volume and cutting out on our 6X (latest software). When we install systems, we always do LAN Host mode, but we used NAT/Firewall with DMZ on ours to see if any problems would crop up. Today our Frac T-1 was spiking at 1.4 or so (it's rated at 1.5) when we were downloading some programs. During that time, we experienced the voice volume and cut out problems. Our carrier is going to monitor our circuit for a time and get back with us.

Today, we looked at the 6X and the two LAN & WAN lights were going crazy. Much more activity than usual. I don't know if this has anything to do with anything...but we're going to watch it and see what we can find out.

A 6X customer with tons of voice call activity (in & out) has experienced no volume or cut out problems at all since it was installed over a year ago. Neither has anyone else that we know of.

The one customer is 7.2.12.2 and the other is 7.3.x

I spent the afternoon checking this out. I recorded calls and used audio editing software to record DB levels with lots of different call scenarios and then compared the DB recordings.

The biggest difference in audio level has to do with the person that's speaking and how they are holding the handset. Both customers complaining were using handset shoulder cradles and are partially covering the mic at times with chin or cheek.
I compared audio levels on different lines, different phones, handset/versus headset and concluded that:
1) it's not analog lines
2) it's not PRI lines
3) inbound calls and outbound calls have the same outbound audio level
4) it's not a bad phone
5) it's not a bad handset
6) it's not bad firmware on the phone or phone system

We suggest the following to correct the problem:
1) Don't cradle the handset on your shoulder.
2) Don't use shoulder cradle pads
3) Consider a headset if you don't want to hold the handset with your hand.
4) Consider taking your handset apart and removing the dust cover from the mic area to increase your mic sensitivity.

Things we are aware of:
1) The older Allworx standard handset has a slightly higher mic sensitivity and higher earpiece volume than the new high fidelity Allworx handset.