I use voiptalk.org in the UK quite successfully. Not had any problems with them and very easy to set up. I have them on my UC320W and also on my iphone (via the Bria app). Works great on both.
If you want to use Voip on your mobile also, bear in mind that some (I think it might actually all of them but not certain) UK mobile phone providers they block Voip unless you pay them more money - so you can either pay them more money or set up a VPN to one of your servers like i did! Obviously you won't have to worry about that with your UC320, just set it up and go!
All the best,
I am looking at replacing a SPA9000 with the 320.
I also use Voiptalk.org, with about 90% success with the 9000.
Thus are you open to sharing your config on the 320? As I am looking to replace the 9000 and a Granstream GXW4104.
Of course, it's a pleasure:
Require Registration: Ticked
Uses SIP Remote-Party-ID: Unticked
Outbound Proxy: nat.voiptalk.org
Only Allow Calls To: (Leave this box blank)
Call Capacity: 2
Prefix dialed numbers with "+44": Unticked
Company Name: (Leave this box blank)
Account ID: Enter your Account ID in this box, e.g. 8442855xx (where the xx are also numbers)
Account ID: Enter your Account ID in this box, e.g. 8442855xx (where the xx are also numbers this is the same number as entered in the Account ID box above)
Password: Enter your voiptalk password for the account number entered above
SRV Record Lookup: Unticked
SRV Auto Prefix: Unticked
NAT Mapping: Unticked
Send Nat Keep Alive: Unticked
Local SIP Port: 5060
It's pretty straigh forward but let me know if you have any problems and we'll see if I can get a number to you to give me a call and I'll try talk you through it.
I just need to get a 320 now!
Will come back when it's on site and I've played.
And FYI - I use Bria for VOIP on my 4s, with VOIPtalk. Used to work but not used in a while.
Bit of an update on using Voip on your mobile in the UK. I upgraded (I use the term upgraded loosely, to be honest, it's more of a downgrade from the iphone 4S ) to an iphone 5 and went from T-Mobile to EE (I know technically it's the same firm) and I can now use VOIP without having to send the traffic via a VPN.
I also realise tha I use brackets far too much!
All the best,
check them out, they provide good quality SIP trunk with 1/1 billing. Email at firstname.lastname@example.org
you will get 1$ FREE credit for testing.