While I thought the Simultaneous Ring option in Digital Voice sounded like a great idea, now that I tried it I found a major fault. I am not able to distinguish if the caller was trying to call me directly or if they were calling my home number. Therefore, I keep intercepting calls I do not want to intercept! There should be a means of identifying the simultaneous ring via a unique ring tone or within the caller id (e.g.., "SR" prefix, etc.)
The issue is that the Caller-ID system passes only the caller's phone number. There is no way to indicate the route a call took to get to the target phone. The caller's name is not passed in the data, instead it is a lookup done by the phone system at the receiving end(*).
Digital Voice could be designed to replace the caller's phone number with the phone number of the line that is set for simultaneous ring. Then all SR calls would come through with your home phone number as caller-ID. That would be quite useless.
If your problem is you're getting a lot of junk calls, look at nomorobo.com. It's a great service available for free to anyone with a simultaneous ring feature. It zaps junk calls after one ring on the main phone line.
If the calls come from the same sources, you could add entries in your cell phone's address book for them. Most cell phones display the name in the address book instead of the caller-ID name. You can enter anything you want in the cell phone allowing you to easily determine where the call came from.
A second line on your cellphone could help, too. But that'll cost you.
(*) If you've noticed that some numbers have different caller-ID names on cell phones vs. land lines, this is why.