G.722 is probably the most widely implemented wideband codec today in VoIP telephony (7kHz/16ksps), so that would be my recommendation for a first step toward adding wideband audio. G.722.1, at 16 - 24kbps, would be a good next step. Although it's only 7kHz, these are still twice (more than twice, in practice) the audio bandwidth of G.711, but at the same bit rate, and they carry most of the voice components that are cut off by narrowband telephony. 7kHz audio will also take advantage of attached mics, speakers, and headphones, so do-it-yourself installations can get surprisingly clear sound.
Please contact me for any questions or clarification; I've been working on this issue for a number of years now. Thanks to your great team for a great system!
www.jeffreyrodman.com (check out the "wideband phones" page for some demos of wideband vs. narrowband audio)