Especial, I want to know which PCI(e)-Cards to connect an analogue hardware phone are well supported / recommended by freeswitch.
Does http://www.asterisk.org/astdocs/node12.html also apply for freeswitch?
Those are expensive, and a IMHO the OpenZAP implementation is still in its infancy and I can't see it getting a strong movement behind it to make it better. External IP based gateway's are much more easier to deal with. I have heard good things about Patton's and AudioCodes and both make some cheap models that are way less money than the digium cards. I set up an SPA2102 for a pair of FXS's I needed for faxing its working flawless, I am just setting up an SPA3102 as I needed an FXO port and that's 3/4 working. Those Linksys devices were very cheap, ~80 CDN I paid for each.
On the other side, are there any features of an analogue modem, I have to pay attention for? Or will any Linux supported modem be okay to dial out?
Linux will support them fine, but that's not the only concern, IMHO you want to avoid those, there is nothing that makes them appealing anymore from my perspective... jlc