where is this PIX hosted by RackSpace? in nepal? probably not, i guess.
to summarize, you need access to a server in a country that does not block ports or domains. you set up a VPN between your network in nepal and the network outside nepal, maybe this RackSpace server. you will need Asterisk to be located outside nepal.
ip phone (in nepal) ==> router (in nepal) =(vpn)=> router (PIX outside nepal) ==> Asterisk (outside nepal) ==> VoIP Carrier
you need to configure the VPN on your router in nepal and the router outside nepal. the only “special configurations” should be necessary on the two routers that create the VPN. a VPN will make all the computers appear to be on the same private network. you should not need any special configuration on the Asterisk server.
the client IP phones do not need any special configuration. they simply point to the Asterisk’s private network address created by the VPN.
the VPN does create encrypted traffic but you do not need to worry about this on your ip phones because this encryption is only between the two VPN routers. your ip phones are not encrypting traffic between themselves and your local router.
the scenario for the dynamic dial-up phones might be more complex. i assume these dynamic phones are soft phones on laptops. you may need to have a VPN client on the laptops. so, the laptop user dials into the internet. then the laptop user opens the VPN client and logs into the router outside nepal, thereby placing the laptop on the same private network as the Asterisk server. or the VPN client could log into your router in nepal. then you configure the soft phone to point to Asterisk.
all of this will probably add some lag to your conversations since traffic must be routed out of the country before it can actually start a call. and using a dial-up connection for VoIP is never really the best solution, broadband offers much better voice quality.
btw, what is the purpose of this set-up? just looking for cheaper long distance rates?