Android - Can I recharge my Android smartphone at any USB port?

There're two flavors of USB ports - powered and unpowered. Unpowered ports can't supply power to the devices and are rather rare. You identify them easily - connect the smartphone to them and see if it starts charging. If it starts charging the port is powered and you're okay.

If the USB port supports USB sticks then it has power to recharge a smartphone. The only question is how much power it has. The USB protocol includes what I would call a "power handshake". Host (radio) and client (smartphone) communicate with each other and the host specifies how many milliampere the client is allowed to use.

If the radio has USB high-power support you will get up to 500mA, without only up to 100mA.

BTW: A plain USB power adapter usually supports up to 1000mA. I assume a simple car 12V-to-USB-adapter would also support that much power.

Therefore even if charging via radio works, charging will take significantly longer. How many milliamperes are used for loading can be seen on a large number of phones by the Battery Monitor Widget or similar apps.

I usually charge mine from the USB port of my TV decoder (that's always powered on) so I think there will be no problems.