Cell C Voice - what does this message mean??

[17seconds]

I received 4 missed calls whilst I was in a meeting today and one more yesterday whilst I was unavailable as well - All from Cell C numbers. (I'm with vodacom)

When I try calling those numbers back the Cell C voice says :
"the device of the subscriber is not suitable for this type of request"

Is it a fax line?

 

[HPFM]

it will most likely be a cellphone router, which is attached to a PABX system to reduce the cost of outgoing calls.

Normally the least cost routing companies block the caller id on these routers, as you cant phone them back in general.

 

[chris2.0]

Yeah, it's called a Premicell, but what I dislike even more - most people hide their CLI on them, so they call you as Private Number...