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In some scenarios you may need to work with an older PBX that has Analog Line (Trunk) interfaces and the PBX has an IVR. Using regular Cisco and Grandstream ATA's may have unreliable DTMF tones going into the PBX IVR. In some cases only some of the DTMF tones get passed and some are missing. This has been a recognized problem and typically takes a lot of trial and error settings changes and even then reliability will not increase. It is best to put a real VoIP gateway in place for these scenarios.

We have tested the following sucessfully:

Grandstream GXW gateways
Quintum/Sonus ASM and AXG Gateways

We believe the Adtran Total Access IP gateways with Analog ports will work, but have not been tested as of this date.