We use to have over 300 remote agents setup using one-x agent (on VPN). We had them setup at one point using VPN Hard Phones, and then switch to softphone (or road warrior I think).
I agree with dclark1111, the hard part is the agent side internet connection, if it is not good then you will have problems with that agents. The other thing to keep in mind is the USB headset, and the Windows OS messing with the audio, you should look at setting windows to not have control on the audio.