Question I've never found a certain answer to: is there a single radio out there that supports both amateur and CB bands? Pretty sure the answer is no due to fundamental incompatibility.
For mobile applications the answer is probably "no" if you are referring to VHF amateur bands. The antenna and modulation requirements are different enough that you'd end up with two different radios inside the "single" radio using two antennas so why bother. You'll notice that a CB antenna is pretty long owing to operation on the 11 m band (HF, aka shortwave, AM and sometimes SSB). The amateur bands you are most likely referring to are VHF using frequency modulation which is perfect for mobile and handheld devices because the antenna can be short.
If you are referring to the shortwave (HF) amateur bands then the issue becomes a legal one even though the technical issues get much simpler. The FCC has rules against operating HF amateur radio gear on CB frequencies, though this is technically possible without the limitations mentioned above for VHF. But you're not supposed to do that and some amateur gear is programmed not to allow it. The primary reason for this limitation is that HF HAM gear can transmit at much higher power, generally speaking, than the unlicensed CB limit.
If you only need to receive, then absolutely there are radios that will do everything from kHz to low GHz, AM, FM, SSB, etc., but you'll still have to use different antennas if you're talking CB and VHF/UHF.
