Have a look at this, it might help:
tpad.com :: View topic - How to use Free SIP Broker DID Numbers with Tpad
How to use with Tpad and Tpad Number:
1. Dial the Sip Broker DID Number (in the format that makes it a local call for you)
2. Wait for the IVR welcome message.
3. Dial *8142 (STAR Key - located below 7 key then 8142)
4. Wait a second and dial *Tpad number of friend (e.g. STAR key then 1126789)
5. N.B - some numbers may ask you to press a "#" (Hash / Pound Key) at the end e.g. *8142*1126789#
6. The Call connects to Tpad Number (if online) or you can call forward to your landline / mobile number via Manage Accounts Page.
Example - UK Call
I dial 6608447 from a landline in Manchester.
I get a welcome message, i dial *8142 then *1126789 (tpad number) then # key.
I connect to my friend in America and i pay for just LOCAL CALL.