I used the Movian client from Certicom on my 3970 with BT/GPRS and WLAN without problems. On the 4700, it broke the Wifi.

I tried the Apani client and it broke the radio too.
Certicom don't support the client anymore, instead they supply a toolkit for you to build your own client. There's a link on the Certicom site to www.anthavpn.com where you can request a demo of a client they've built with the Certicom toolkit. I tried it on my 4700 (rom 1.10) and it seemed to work. The UI is not very intuitive, and it left the wifi icon on the 'ipaq wireless' page orange (even when successfully registered to my AP), but it did seem to work.
Apani told me their next release will support GPRS, but not the 4700.

They did tell me they would support it at some stage though.
WM5 might change things before then...

although it may be for the worse
Dox