Check out sipgate's own configuration guide.
http://www.sipgate.com/faq/article/397/How_do_I_set_up_my_VoIP_device
You need to input these parameters in your spa1001's admin page
* Domain/Realm: sipgate.com
* SIP Proxy: sipgate.com
* Outbound Proxy: sipgate.com
* STUN-Server: stun.sipgate.net
* STUN-Port: 10000
* Register Expire Time: 600 Seconds
* Username: the device ID
* Authorization User: the device ID (e.g. 1234567e0)
* SIP-Password: your SIP-Password
To get info for the last last three items
* Click on My Settings. (in your sipgate account)
* Place your cursor over the phone and then click on SIP Credentials.
* All the information you need to enter is displayed in the following box.
To enter the parameters in the sp1001 admin page
go to the "Device configuration" at right of of the guide, and take a look at all of the the LinkSys devices listed there. SPA1001 is not listed there, but after you see the other devices, you can get the idea.
After that your phone should be green in your sipgate's account.