Hi,
the callout radio altimeter alive aims to enhance flight crews terrain awareness and should always be done regardless of the radio altimeter callout settings. If you don't get the 2500 call (two thousand five hundred) you have to call this one too as pm. Have a look at the Airbus FOBN supplementary technique - altimeter setting - use of radio altimeter. I'll post the link later on when I clear the jet lag ;-)
Cheers