interfaces for sending FAX ?

[marelin@gmx.ch]

(i'm not onlist, please cc to me)

I would like to send FAX from Germany and Switzerland.
I am used to work on Debian unstable.

I don't have a real fax modem, only a standard 56k one 
for serial dialup. Can i use this too ?
This is an analog phone connector, but this ends in a ISDN 
converter way down in the cellar. I can't imagine to climb
down there with my laptop to send a fax, anyway. 

Is it possible to do FAX via my ADSL network interface ?
This would be much more comfortable.
I know there are online services but AFAIK i would have to
pay a subscription.

What are my options ?

thank you in advance

maren