during my pstn gateway survey, some people asked about cheap PSTN gateways. Let me share what I know, speak up if you know more.
analog ------- AudioCodes and AlliedTelesyn provide SIP FXO gateways wuith four ports for about $1000. We have both of them in our lab (i.e., they do exist) but haven't tested them yet (i.e., we don't know if they work).
MediaTrix might have some too, perhaps sightly cheaper, but they denied shipping to us as we are not in their interoperability club (which makes me cautios about their interoperability).
arrayvox was claiming to have some very cheap ones, but I neither know if they shop nor if they work. The same for welltech.
in general, not only is a challenge to make the sip part of it work, but also the analog -- tone recoginition may be pretty challenging. It differs country from country and pbx from pbx.
digital ------- I don't know -- some people meant Asterisk would do that, some other meant not really.
other ----- someone told me vegstream (both digital and analog) was good and afforable. more can be found at http://www.iptel.org/info/products/index.php?category=gateway&name=Gatew...
-- Jiri Kuthan http://iptel.org/~jiri/