To set up CSIPSimple for Voiptalk, all you need to do is create an account with the following settings in Expert Mode!
Make sure that you replace the bits in bold with details from your account.
And watch for the colon in the Registration URI, it's definitely not a dot!
If you don't de-select the Allow Contact Rewrite, the application double-registers with VoipTalk, and confuses the system, particularly when you check online to see if you have connected or not.
Account Name: Descriptive Account Name
Account ID: Your Name <sip:firstname.lastname@example.org>
Registration URI: sip:voiptalk.org:5060
Data (password): ********
Proxy URI: sip:nat.voiptalk.org:5065
Allow Contact Rewrite: Unticked