When HSDPA was first specified it was unfortunately forgotten to put an indicator somewhere on the broadcast channel so a mobile could distinguish a 3G network from a 3.5G HSDPA network and show something to the user. It was added in a later release of the standard but I haven't seen a device yet that would do something with the information or networks that would actually broadcast it. Turns out that quite some networks have this turned on by now and some phones like for example the Nokia N72 display "3.5G" instead of 3G permanently and not only while an HSDPA data transfer is ongoing. How nice, but it's too late now. Some network operators use HSDPA now but have chosen not to activate the indication, hence, the E72 still shows 3G despite the network being HSDPA capable.