Tried plustalk using the xlite software and very hit and miss reception. Not reliable enough for serious use. So 'borrowed' a phone from work.
The setup is asking for the following;
SIP Server: (e.g., sip.mycompany.com, or IP address)
Outbound Proxy: (e.g., proxy.myprovider.com, or IP address, if any)
SIP User ID: (the user part of an SIP address)
Authenticate ID: (can be identical to or different from SIP User ID)
I've tried various here, including for sip user id, my 6 digit number and 'plustalk'. Using sip.force9.net for the sip server and nothing for proxy though tried sip.force9.net again.