Yes. See the manual pages for slattach(8), sliplogin(8), ppp(8), and pppd(8). ppp(8) and pppd(8) provide support for both incoming and outgoing connections, while sliplogin(8) deals exclusively with incoming connections, and slattach(8) deals exclusively with outgoing connections.
For more information on how to use these, please see the Handbook chapter on PPP and SLIP.
If you only have access to the Internet through a ``shell account'', you may want to have a look at the net/slirp package. It can provide you with (limited) access to services such as ftp and http direct from your local machine.