internet connection triggered by (voice) call

Hello,

one or two weeks ago, I posted a message here, that I was looking for
routers, which are able to connect to the internet triggered by a normal
phone call and register the ip address at dyndns afterwards.

I have posted, that I found 2 routers, a draytek and a zyxel. I bought
each, but unfortunately

- the draytek router goes into the internet only by calling from one
preconfigured phone number (so only a single user or phone can trigger it)

- the zyxel cannot trigger it by a normal call but needs a RAS
connection (though the sales department told that it would work).

All other vendors (at least 11) also do not have this feature (which
works with pc running linux).

But what about 3com? They are using Linux and the source is available.
3Com told me, that the routers cannot do it. But what about implementing
this feature self? Has anybody experience with this?

Greetings

Ernst