I stole this interesting comparison/contrast between VoiceXML and VoicePHP from Yusuf Motiwala's Facebook status. (Hope he doesn't mind!)
http://is.gd/eBvV & http://is.gd/eBwc
What do you think?
And btw, two conferences approaching fast that are must attend are ITEXPO / 4G Wireless Evolution / Digium | Asterisk World conference in Miami Beach, Florida Feb. 2=4, 2009 and 17th Annual Convergence India in New Delhi, India March 18- 20, 2009. More global information technology and IP communications events are listed at http://www.didx.net/events and http://www.tmcnet.com/channels/did-ddi/.
(... browse some of our team's other blogs at http://blogs.didx.net and http://blog.tmcnet.com/monetizing-ip-communications/. You're welcome to comment, contribute, and collaborate any time.)