The first episode of (British) Who Wants To Be A Millionaire? had a couple of tiny little changes from those which followed: specifically, there was a physical cordless phone which was used (possibly as a prop, possibly as required technology) when the contestant phoned a friend, and the "ding-ding-dong" locked-in-answer sound effect for the 64,000 pound question was very slightly more elaborate, possibly described as "ding-ding-dong orchestral slide". We only ever heard this more elaborate sound effect once. Incredibly incidental and inconsequential, but rather fun.
Twiddly-dee,
Chris