There is a standard headphones jack for a headset on my IP telephone,
and I'd like to connect an answering machine to it. The trouble is I
can't find any answering machine in stores that has the headphone
jack. Also, couldn't find any regular answering machine for IP
telephones in VOIP internet stores.

Did someone try to convert digital dictaphones into the answering
machines ? These days there are dictaphones which start recording when
initiated by voice. Likewise, I was thinking when a dictaphone
receives a signal from a telephone perhaps it can playback an audio
file as a greeting message and then record caller's message ? Are
there some wild hacks to dictaphones ?

Is the only remaining option to subscribe to some voice message
service ? No more home answering machines ?

Thank you.