I dont think that's the case.
The two antenna of U960 can be simultaneously active. In the traditional Dual Sim Dual Standby phones, only one line can be active though both lines are standby.
The practical illustration is if line 1 can be used to call through line 2 on the same phone. This is the case for U960 according to the demo I have seen.
Re: Motorola XT-532
I don't care about whether it's DSDS/DSFA, but I can confirm that for XT-532:
1) it's not possible to be talking on line 1 and also receive calls from line 2. (i tried the test kengcedz suggested, calling line 1 with line 2. The phone is engaged).
I went to Moto customer service. They confirmed only one line can be active during a call. They gave me a stupid example of a hot and cold water tap. Both hot water and cold water can be readily usable, but the tap can only discharge either hot or cold water only.
2) Maybe other XT-532 users can confirm. When calling using line 1, line 2 will be disabled. A stop sign (similar to a no smoking sign) will appear above the line 2 reception bar.
When you're talking on line 1 already, if a person calls line 1 (line is engaged or if you have call waiting, you can pick up of course) but if a person calls line 2, the caller will receive an out of service/coverage reply.
This defeats the purpose of having a dual sim, i'm better of with two phones. When i'm on a private call, no one can call my work mobile number. Call waiting would only work if my boss calls my private number. If he calls my office mobile, it would be out of service and i would never know he called~! (For this reason i'm sticking to my old non-android B7722 for now).
3) With my old Samsung B7722, using line 1 i CAN call line 2.
4) But if it's not important for both lines to be simultaneously active during calls then this phone is great. I.e. going up to Milan to Lugano.
I'm gonna look for the u960.