Binding radio calls is both easy and very useful. Having to go through a list every time is not good in the midst of battle. Also, radio calls bound to a key can also have custom text added to them (instead of the default text you get when using the radio list)
Radio commands are invoked using the command 'ut_radio' and the list is from 1-9 (not 0-8).
A few examples of mine:
\bind b ut_radio 5 1 I sees dem @ $crosshair <---- Enemy spotted
\bind h ut_radio 3 3 I needs ^1<3 ^2$health <---- I need a medic
\bind F3 ut_radio 8 1 I'ma go ^1red <---- Heading to bomb site A
\bind F4 ut_radio 8 2 I'ma go ^8black <---- Heading to bomb site B
\bind F5 ut_radio 4 9 Meow! <---- How the hell are you
\bind F6 ut_radio 1 6 I'll be there soon <---- Medic on the way, hang in there
Obviously ^1, ^2 and ^8 are colours, red, green and black respectively. B and H are text macros assigned to the two thumb buttons on my mouse.
You will also notice $crosshair and $health, these are variables you can call upon. $crosshair will announce the location your crosshair is pointed at and $health will announce your current health.
Go here for a full list of radio calls, and the variables list: