My guess would be that the Huawei didn't drop down to 3G for the call when its network mode was set to auto because it considered the 3G signal too weak, whereas when you force it to use 3G only, it has no choice, and has to use whatever 3G signal it can get.
It is normal for the Huawei to take a while before an outgoing call connects, because it is waiting to see if you dial any more digits, before it is confident you've finished entering the number you want to call. It then goes off and sends the full number to the mobile network. One thing I discovered when I used the Huawei in the past is that if you put a # at the end of the number, it takes that as a sign you've finished entering the number. So try that, and I think you'll find your calls will connect a lot faster. I'm guessing the Tenda is doing something a bit more intelligent rather than waiting. For example, maybe it's been programmed to know that an 07 UK mobile number is always 11 digits, so it then just transmits the number to the network the moment the 11th digit has been entered.
In answer to your question, Three/Smarty have indeed cut themselves off from 3G phones (apart from the odd place they've not yet turned off the 3G), as have EE and Vodafone. The networks are literally turning off the 3G hardware at the masts, so this is not something a phone or router can force the network to switch down to, unless you are in one of the few places where the 3G has not yet gone.
It is normal for data not to work on the Huawei when it's on a 3G call.. I'm guessing it doesn't support calls and data at the same time.
