I'm trying to drum up support to get Cisco to identify and fix lagging DTMF issues in various Cisco SIP phones. I've mainly been working with 7800 series phones lately (with both CME and CUCM). The lag issue primarily appears when users have to enter a sequence of digits after their call is connected. For example, logging into voicemail, interacting with IVR systems, entering PIN codes, conference bridge codes, etc. The issue is that the phones start lagging in responding to button presses, causing end users to enter the wrong digits or the wrong digits being sent to the system they're interacting with. I've verified with debugging that the problem appears phone firmware related, as there is delays in the actual digits being received by the call control device.
Has anyone else noticed this issue? Just place a call, and enter several sequences of digits rapidly (for example, 123456789*0#). You will notice the phone seems to buffer button pushes, and delays in the phone giving a confirmation beep (or the actual DTMF tone if you are using the handset) back. Also, the issue seems to be worse when using a handset vs speakerphone, and when there is audio being received on the phone.