Not sure what exactly you are asking, See my 2 cents inside.

I assume that you have one working SPA1001 already, and now you want to test the new one.

To make things simple, just clone the all setup from existing working SPA1001 to the new one except the following setting:

- leave "Line 1" and "line 2" "enable" unchecked on the new SPA1001. I believe it's on top of page on "Line 1" and "Line 2" tab of SPA1001 configuration. If you only use one VOIP provider, you just need to setup line 1.

Check other seting are identical in the both the existing working SPA1001 and the new one. Then upplug the working SPA1001 from you network, and plug in the new one and enable line 1 & 2. Test the new SPA1001 as you wish.

If you set up static IP address for your existing working SPA1001, certainly you need to do the same before you connect the new one in your home network.

To answer your original question, you can't have two ATAs that have the same account setup in the network regardless their IP addresses. As both ATAs will try to register using same credential(user name& password) at the VOIP provider server, the server will be confused. Hence, there is chance it doesn't know which ATA it should deliver the incoming call to when someone callls you.

If you have two VOIP providers, say A & B. you can set any of the following:

- SPA1001 #1 setup w/ A & B

- SPA1001 #1 setup w/ A while SPA1001 #2 setup w/ B

You just can't set the same account at more than one ATA at same time.  It's the same problem when you set up a soft phone on PC while using the same account setup with ATA.

Hope it helps.