The "problem" here is direct point-to-point calling vs "server based routing".
Older endpoints like the VP200 had your home IP address entered into the iTRS database. Your router allowed an inbound port connection for H.323 call setup, which let someone call the VP200 from the Internet.
H.323 "facility redirect" isn't supported by all videophones, so Sorenson couldn't get away with simply redirecting incoming calls to a central videomail server.
If your home router is down, inbound calls can't make it to the phone, so the called party recording a videomail message isn't possible in that model.
Instead, Sorenson made their "signmail" solution which records the message on the calling party's phone. Meaning, if you are a Sorenson customer and call another Sorenson customer phone that is either not online or is busy, your phone records the message locally and then uploads it to Sorenson to be delivered to the called party's Sorenson phone when it becomes available again.
The problem with this model is that nobody else has access to this proprietary Sorenson signmail system. There are no publish APIs for other VRS providers to interface with. It is entirely proprietary and closed. This mechanism is also entirely bizarre, and not used by any other VoIP solution on the planet. Nobody else does it this way. Anywhere. If you don't think this was intentional, I'm not going to try and convince you otherwise.
Most VRS videophones today, including the newer Sorenson nTouch phones, register with "gateways" on the Internet that are run by VRS providers when they are turned on.
These gateways have their IP addresses entered in the iTRS database for those phone numbers. This allows calls to those phones to be routed to cloud servers which can then record voicemail messages if the called phones aren't online.
Sorenson is finally putting a nail in this coffin by finally ending Signmail support for the VP200 videophones so they no longer have this interoperability barrier.
You can find Sorenson's ECFS filing of notice of substantial change for that here:
http://apps.fcc.gov/ecfs/document/view?id=7521366519
Pursuant to 47 C.F.R. § 64.606(f)(2), Sorenson Communications, Inc., (“Sorenson”) hereby notifies the Commission of a substantive change to its TRS service. On May 14, 2014, Sorenson ended SignMail support for its VP-200 phones as part of its plans to end support of VP-200s. Sorenson has made ntouch phones, which continue to receive SignMail support, available to all VP-200 users since 2011, and continues to offer them to any remaining VP-200 users. Sorenson is aware of fewer than 5,000 VP-200s still in use. Sorenson does not believe that this change will affect its ability to meet federal minimum standards.
This was filed July 3rd. Sorenson claims fewer than 5,000 VP-200s still in use.
It is also finally enabling the same functionality in nTouch Signmail that has been available for all other VRS providers for years now: the ability to record messages on a cloud based voicemail server instead of on the calling party's phone. This may be related to the new nTouch version 4 update as per this recent filing:
http://apps.fcc.gov/ecfs/document/view?id=7522900740
Pursuant to 47 C.F.R. § 64.606(f)(2), Sorenson Communications, Inc., (“Sorenson”) hereby notifies the Commission of a substantive change to its TRS service. On or around July 23, 2014, Sorenson began rolling out version 4.0 of its ntouch software. Sorenson expects to upgrade all users over the course of approximately six months to one year.
I honestly have no idea if any of that is required for cloud-based videomail recording to function. They don't say as much in their filing.
Full disclosure: I no longer work in the VRS industry, having left it for a startup over a year and a half ago, but I still keep up with what is going on.