The official CIA Local phone (www.cia.com) phone adpater is  Linksys SPA2102/SPA2100, but you can use Grandstream HT486/HT496/HT502 as well. Here are the step by step how to do the configuration:

Step One (Registration)

1. Got to http://www.cia.com to register the Home phone service. Pickup " FREE CIA Home Phone Basic" which is $3.95/month(system access fee). Fill the the registeration form;
2. Select "I already own a Voice Terminal Supported by CIA.", then select "Linksys SPA2102 Voice Terminal" in the drop down list;
3. Select "I'd like to get a brand new phone number from CIA (No Additional Charge)" when you pickup phone number;
4. Make the payment.

AFTER some time, it will be a few hours or a few days, you'll receive an e-mail from CIA which tell you the online account number and the password for CIA phone.  THIS IS NOT THE VOIP ACCOUNT NUMBER YET.

Step Two (Config Grandstream Voice Terminal)
1. http://myaccount.cia.com/ and login with the account from CIA. Make sure you phone service status is "Active";
2. Click "Register / Update My Voice Terminal" link;
3. Input the MAC address of your ATA, it can be any MAC address which doesn't conflict with others (i.e. 0123456789012 ). You can find yours on the bottom of Grandstream ATA. Click "Submit MAC Address" button;
4. Open your Internet Explorer (CAN NOT use Firefox) and past this link:
http://voip.cia.com/provision.php?MAC=0123456789012
(Replace 0123456789012 with your own MAC you registered in step 3);
5. Follow this screenshot. Don't forget to change the DTMF setting from default to the option in screenshot, otherwise your voice mail will not work properly.
http://sunnyvoip.googlepages.com/GrandstreamCIAconfig.jpg