I am not aware of the Strata DK having any VoIP capabilities at all. Toshiba developed all the VoIP with the CTX and the CIX line of systems. Back in around 2002 when the Strata CTX was released, and the DK series discontinued, VoIP was still a relatively new concept and not very mainstream. It did exist, but it probably did not make sense to add it to a product line that was about to be dropped.
There may be 3rd party solutions for adding VoIP technology to the DK, such as the
https://www.citel.com/products/portico-tva/. This is basically using the digital phones and extending them across a network. I have seen something like this at a customer location that had phones connected to another building. We eventually replaced this with VoIP phones on a Strata CIX.
If this person wants to add VoIP, Toshiba is often having trade up promotions. Right now I think it is for the IPEdge and App server, which is a nice voicemail upgrade with new features including voicemail to email. You can reuse the cabinets and most cards and phones if you upgrade the processor to a CIX670.
I would like to add the VoIP is a bit of a broad term. You can use VoIP to extend the reach of desk phones using IP to another building or across the globe. Also sometimes IP phones are used just to combine voice and data networks to reduce infrastructural costs. You can join multiple PBX systems together (QSIP) using VoIP. You can replace your analog phone lines with VoIP lines (SIP trunks). On the PC you can make person to person video calls over the internet (Skype, etc). People sometimes think VoIP means free phone calls. And sometimes people use VoIP to describe the extra features you often get with an IP PBX, such as previously mentioned Voicemail to email (Unified Messaging), follow-me, hot desking, etc. Usually if I am asked about VoIP I ask the customer, "what do you want it to do?"
