Webslinger: I agree with UseTheForce's reply, with regard to the value of this feature.
You may have some marginal improvement when using a high-quality telephone plugged into the ATA, but you are discounting the fundamental issues: the hardware and the PSTN limitation. The PSTN as of now, isn't designed for wideband audio, and the G.711 PCM codec already covers the theoretical maximum audio range that can be transferred across the PSTN. The majority of analog telephone handsets can't reproduce audio better than that, anyhow. Unless you have end-to-end component support, it's like playing a HD, lossless audio recording through a 5 dollar set of earbuds, or listening to AM/FM radio over a $1000 headphone.
I'm not disagreeing that it would be nice to have, but it is largely useless at this time. I assume Obihai will add it sooner than later, since they've already got it working on the other devices. There just isn't much point to it with today's analog telephone handsets and PSTN network. The industry is still bickering over which AMR-WB codec will win, and that's another reason to let the dust settle a bit. There are some licensing issues that are being hammered out.
A great example of this is the OBi 1032 IP phone. Unlike your DECT 6.0 phones, which can't possibly compare, given their audio compression and wireless connection, the OBi IP phone was engineered from scratch to include the electronics and speaker/microphone components necessary to support wideband. I have the OBi phone, and I have a Panasonic DECT 6.0 phone, and the difference is astounding... there's no way a DECT phone can come anywhere close to that. Connecting a DECT phone to an ATA like an OBi involves way too many analog<-->digital<-->analog<-->digital conversions, on top of the wireless connection's limited bandwidth.
Even the inter-operability between the various mobile phone carriers' implementation of HD Audio is going to take some time to work out (in the USA, I am talking about AT&T vs. Sprint vs. T-Mobile vs. Verizon). They only recently agreed to cooperate on working on this. In another example, Google Hangouts supports wideband audio, and eventually, the goal is for them to inter-operate with other carriers that support the same codecs, but it's going to take a lot of cooperation between the industry players.
Do you know of any SIP Internet Telephone Servivce Providers that support AMR-WB codecs at this time? If so, the only way you would benefit would be if you had a WB phone on both ends and both parties were using the same SIP ITSP.