In this environment, it becomes possible to make voice calls without specialized DSP hardware by instead using PC-based software.
This allows speech applications to scale to large numbers of concurrent calls, without bogging down the host CPU.
There are a significant number of voice, speech, conferencing and fax applications that have been written over the last decade.
This often means that backward-compatibility is a big issue, since if possible users want the applications to migrate seamlessly to the VoIP environment.
This usually means that HMP products expose one or more standard APIs that historically has been used to write telecom apps in the past.