Are mobile phones used as a tethered USB modem for the computer, successful or what?

Yes.almost all the smart phones can.from nokia 6600 to upward and some other brand's mobile phones.if your phone comes with a data cable and CD ,you can use most of them as modems.I have used n70 but maximums speed is 512Kb/ps .If your phone cannot be charged using the data cable,using it as a modem on computer drain its battery very quickly.Using a Bluetooth instead of the USB is more comfortable .After two batteries and two chargers dies because i've been charging the phone like always due to the power it drains when used as a modem,i decided to buy a HSDPA dongle