Ice is catered as ice. Have not seen any manufacturer offer an onboard icemaker yet, but thats not to say they don't exist (if you ever visit the Aircraft Interiors Expo in Hamburg you'll realise that everything has already probably been invented for inflight use, no matter how obscure or useless we might think it is).

Tea/coffee makers run off the potable water supply run through a standard electric heating filament. The potable water supply in turn runs either off a pump system or off a pressure compressor system, depending on the aircraft type. It is sometimes questionable which one of the potable tanks or the blue juice tanks is nastier.