really? I thought that had been postponed, anyway, if it has been upgraded, the new garmin definitely has hidden sub menus for the intercom to tweak.
There is a limited time exemption for sporting frequencies - see CAP 1606. If you require to speak to any other stations you are supposed to have an 8.33 capable tranceiver. Ground stations used by GA have started to convert to 8.33 channels to save cash - the ground station's licence fee for 8.33 is 1/3rd of the fee for a 25 kHz freqency. Old Sarum is an example that changed recently. It is expected that most will change this year at licence renewal.
Sidetone is a radio function that feeds back some of the microphone signal to the headset when transmitting so you can hear what you are saying. It is not an intercom function. 8.33 radios when used as the intercom usually have separate settings for intercom volume and squelch which are entirely unrelated to sidetone.
Where loudspeakers are used instead of headsets (i.e. gliders) the sidetone volume is usually set to minimum / zero to avoid feedback howls.