> In the future, my provider will switch from slip to ppp (with dynamic=20
> IP-addresses). So my IP address is no longer known.
> 
> What do I have to do to connect my TT with my PC (permanetely) and my PC=20
> with my provider (temporalely) and what IP addresses should I use?
I never tried it myself, but I think you should at least anable the
GATEWAY option in your kernel config file. The man page of pppd contains
some explanation how pppd can be made to accept an ip-number from the
remote-host.
Did you browse the FAQ-pages of NetBSD (start at www.netbsd.org)?

Leo.