You can easily add SIP.US as a sip trunking provider to your AT&T Synapse Device by following this guide!
Create a new Sip Account, giving it a descriptive name. Set the "Account Type" to "Sip Trunking"
Under "Basic Settings" add the following settings:
Account Enabled: Enabled
Account Name: The name you gave it when you created the Sip Account
Max Calls: Set this as equal to the number of channels that you purchased from SIP.US
Display Name: Enter anything desired or leave blank
User Name: Enter your SIP.US Trunk #
Auth User Name: Enter your SIP.US Trunk #
Auth User Password: Enter your SIP.US Trunk Password
Primary Number: Set this to the DID you purchased from, or ported to, SIP.US
Under Registration Settings Enter the Following:
Registration Type: Dynamic Registration
Registration Expires: 3600 (Can be set shorter if desired)
Under Server Settings Enter the Following:
Address or URL: gw1.sip.us
Address or URL gw1.sip.us
Under Codec Configuration Ensure ONLY G711u and G729 are in the enabled column
Enter Dialing Rules that Match Your Desired Dialplan
***Ensure that routes which are outbound to numbers in North America other than 911 and 933 are prefixed with a 1 when they are sent to SIP.US. We need to receive 11 digits (ex. 1-555-555-5555) to connect the call.***
Repeat steps 1-6 with a second unique name, changing only the URLs in Step 4 to gw2.sip.us. This will ensure that our service is redundant in case gw1.sip.us were to be unreachable.
You have now successfully configured your device. It's time to make some test calls! If you have any problems, be sure to use the link at the top-right of your account to open a support ticket.