Echo is not the best word to describe the issue, but it is how users are describing it to me. The users of IP phones instantly notice that they can hear their own voice louder in an IP phone than a digital keyset. There also appears to be a very slight delay. Is anyone familiar with this issue?

Echo...ahh
Echo can happen when VoIP is used mainly anytime that there is a hybrid in use. Let me explain.
Reflection plus delay = echo. What is reflection, some refer to it as talk back or side tone. On a normal phone it is where you can hear yourself talk through the receiver. Reflection is present on any analog phone so it is considered normal audio characteristic, if you ever picked up a phone and couldnt hear yourself in the receiver it would seem weird. So now we try to have reflection in delay intensive networks (at times) and we now induce this delay to the reflection and this equates to echo to the human ear. It is the same talkback, it is that it is delayed thus the echo sound. An analog handset actually has 4 wires, one pair for Tx and one pair for Rx. This is converted to a two wire virutally combining tx an rx onto two wires (tip and ring), this is known as a hybrid. Anytime a hybrid is involved, reflection is created. Most times the delay is very minimal so the reflection is acceptable.
2 Wire: Loop Start Trunk, Ground Start Trunk, Analog PBX port, IPSLA, etc
4 Wire: any digital station port, T1/PRI, IPRC, etc
Hopefully that helps a bit to explain where echo comes from. Sometimes you can fix it sometimes you cannot. In my experience, elimiate hybrids and reduce delay as much as possible and you should be able to provide toll quality voice via VoIP without a problem everytime.

Excellent explanation. Thank you. By your definition, I don't believe I have any hybrids. All user phones are either digital keysets or IP phones. All analog devices run to an SLC. I use all T1s for trunks. What suggestion do you have besides the hybrid? I've made sure that the echo suppression is enabled. The Echo Suppression Sensitivity Level % was originally set at 60. I've tried 0, 25, 75 and 100. Honestly, I can't hear a difference.

I have an axxess system running nearly 100% voip phones with a very few analog extensions and digital sets. We sometimes have the same echo delay problem on our IP sets. It affects individual calls but only occasionally - not all calls and not all extensions. I would also like some suggestions to try, I have not previously tried to address this.

Given the fact that you do not have any hybrids, the next thing to investigate is the network, it's design and it's performance. First though ensure that your endpoints and your card are on the most recent release of firmware. As far as network performance goes, please do not take offense, but that is the next troubleshooting step to take. What you need to verify is that the performance of the network is up to snuff. To support quality VoIP the network must support:
less than 1% packet loss
one way delay is 80ms or less
jitter is less than 40ms
If you do not have any mechanism such as VoIP readiness check software, measuring these over any time frame with any reliablility is difficult to do. A few things that are easy and HIGHLY recommended:
Put your voice on a dedicated VLAN
If RTP voice is to traverse any WAN links, use QoS to prioritize the RTP, the IPRC/endpoints can mark packets with DSCP/IPPrec
Use quality switchgear, a netgear/wal-mart special is not going to cut it; depending on the size I would even use L2 QoS (CoS)
If you are strictly in a LAN environment, these network performance benchmarks should be relatively easy to meet. And as always, junk cabling can ruin it all even with big iron cisco gear powering the network.

I believe the OP is describing 'sidetone', not echo. If the IP fones are 8662's or 8622's and are using the newest firmware, you can HTML into the fones and lower the sidetone level. The fones are shipped w/ the sidetone maxxed out, which is probably dumb on Inter-Tel's part.

Depending on were you are running the phones would determine the best next step. If you are running them inside the office I would set the phones up in a Vlan environment. Across the WAN I would use QOS such as Diff Serv. Outside the office across the internet is an entirely different animal

Thank you all. So basic network troubleshooting for IP phone echo, not specifically with the PBX and endpoints other than ensure on latest firmware. Got it!

Sorry for hijacking the thread, I figured I had a similar issue.