Hello,
The Lightstreamer client library should work without any modification on the iphone browser.
Could you please try one of our demo on your phone (e.g:
http://demos.lightstreamer.com/StockListDemo_Basic/ )
If it does not work, can you try it connecting directly to the internet? (i.e.: avoiding the VPN)
Is the client library in use the one that ships with server 5.1.1?
Let me know what you find out; if nothing helps we might have to enable logging on the phone.