App recording VOIP calls is possible, see Call Recorder - IntCall for instance. There may be others too
Non app based services that record VOIP calls seem to be more - Dingtone, for example
What is common for VOIP recording and different from voice recording is that VOIP recording is done when it is routed through the servers provided by the app (see description in both links above). Ordinary voice recording is not bound by such limitations and can be natively record if enabled on device (I haven't found any reason why routing through third party servers is required and will update of I find)
Perhaps, routing the call through third party servers has legal and security implications besides being a technical limitation to natively record on the cell phone