It really depends on which codec you're using. We had an implementation of G.711, which is not bad, but far from great. However, the license costs for implementing G.729 were so outrageous that my previous company simply couldn't afford it (or wouldn't). G.729 offers better call quality for the same bitrate, or similar call quality for much lower bitrate. Typically, G.711 would use ~64Kbps, whereas G.729 can achieve the same call quality for ~8Kbps (there's also a variable encoding that scales between 8 and 32Kbps). This being said, G.729 also requires a lot more CPU processing power.

If I'm not mistaken, each party of each leg of a call needs a license, which means that for a typical call centre with an IVR server between the agent and the customer, you need:

Summary:

- PSTN converter to IVR: 2 licenses / per customer

- IVR to agent: 2 licenses / per agent

- IVR to supervisor: 2 licenses / per supervisor.

It's pretty normal to see 300-agent call centres, and you typically want at least 300-900 calls waiting. Let's say there's between 10 and 30 supervisors.

300 * 2 + 900 * 2 + 30 * 2 = 2460 licenses. At $6-10 per license, that's more expensive than most hardware PBX solutions alone!

For IVR companies that handle multiple hundreds of thousands of calls per day, it's not really worth it.

Edit: Formatting