Just downloaded a free SIP softphone client called iSipSimple from the iPhone Apps store. Just go into 'Accounts' in the client and set it up as follows to work with voipfone:

Display Name: 056xxxxxxxx (or whatever you prefer)
Domain: sip.voipfone.co.uk
Username: 30xxxxxx
Password: xxxxxx

A fairly basic client, but worked first time with default settings. You can access 'SIP' or 'Cellular' from the same keyboard. There is a more advanced version called iSIP which you have to pay for.

Installed it today and tried it. I confirm that it works well, but is basic. Have you tried other SIP apps?

I haven't used any other SIP apps on iPhone. I do use X-Lite from Counterpath (www.counterpath.com/x-lite.html) on my Windows XP PC for use with voipfone. This has many more features than iSipSimple but there is no iPhone variant as far as I know.

The full iSip app works very well with Voipfone and is very easy to configure, username, password and sip.voipfone.co.uk was all I needed

Another one that works very well is Acrobits softphone, which I've been using, it's a paid app:

http://www.acrobits.cz/products/acrobits-softphone/

Currently it uses push-notifications for incoming calls, which does work though is a fairly inelegant way of handling it (but previously was the only way because of the lack of multitasking on iPhone). It'll be upgraded with full full background operation once they update it with IOS4 multitasking ability. If you want/need G.729 codec it's an additional in-app purchase.

They'll soon be coming out with a "Business" version too:

http://www.acrobits.cz/products/acrobit ... s-edition/

I looked around at them all and it seems the nicest one in my opinion. I've no connection with them, just a user. Since then though, Counterpath has released an iPhone edition of Bria, but I haven't tried it yet:

http://www.counterpath.com/bria-iphone-edition.html

Has anyone tried Session Talk? (http://www.froute.ltd.uk/manual.html) and if so any idea on getting the settings to work?

So, further to my comment above I have manged to get the outgoing calls sorted out and the quality is ecellent but struggling to get incoming calls - has anyone else come across this problem?

iSip have just updated theapp on the Apple store to support multitasking on OS4. Seems to work.

I get an echo or small delay on fring, will i get the same on isip? just wondering if its my wifi causing me the problem or the app?

Acrobits have released the business version of their softphone - Groundwire:

http://www.acrobits.cz/products/groundw ... -business/