There are hundreds of (paid) services offering SIP to POTS that work with any SIP client. I won't mention names, just google "sip callout". That is the big advantage of an open protocol - choosing a service doesn't lock you into a client. (See the post on XMPP above - that sounds like an interesting alternative to SIP.)
There is one application of email that needs to go away: sending status updates or a cool picture to all your friends - especially when forwarded. That belongs on a blog or similar where only interested parties see it.
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There are hundreds of (paid) services offering SIP to POTS that work with any SIP client. I won't mention names, just google "sip callout". That is the big advantage of an open protocol - choosing a service doesn't lock you into a client. (See the post on XMPP above - that sounds like an interesting alternative to SIP.)
There is one application of email that needs to go away: sending status updates or a cool picture to all your friends - especially when forwarded. That belongs on a blog or similar where only interested parties see it.