Don't know the phone, but if it didn't come with a 3G radio, then I'm afraid you're out of luck as the radios are hardware (and related software) that's built into the phone.
Have to say, I'm kinda surprised anyone makes a 2G only phone these days: have you checked the settings? Don't know the version of Android it has, but there should be a setting somewhere that lets you can select 2G only - maybe that was somehow set and you can unset it?
