To the best of my knowledge when the term 'radio' is used then the station should be addressed as 'RADIO' not Tower and the station should respond as as 'This is *** RADIO. It means that an Air/Ground service exists and the only difference between 'Radio' and an a non-radio field is that the station may offer information such as advisory QNH, wind direction and active runway and other known traffic operating in the vicinity. The term 'your discretion' is the key and thus any advice then is unambiguous and pilots should then treat the facility in the same way they would an non-radio, uncontrolled airfield. I understand if one holds an RT license then one can operate an Air/Ground Station.