Sorry I'm late...
I can only answer for Swap Shop and Tiswas. Tiswas began in Jan 1974 (only in the ATV area) and in the only surviving episode of the first 4 years (30th August 1975), a viewer is shown talking on the phone to John Asher. The Swappie began in October 1976 and as we know utilised phone calls from the outset.
CT's "Sorry Noel" on 'Reunited' was in answer to Noel's claim on 'It started with...' that Swap Shop was the first ever TV show for Kids on a Saturday Morning, when in fact Tiswas was almost 3 years old by the time Swap Shop came on air (LWT's 'Saturday Scene' and HTV's 'Orbit' beat Swap Shop to it too!).
Throughout the early years of Tiswas, they used a phone-in device called the "Welly-Phone" (a phone embedded in two conjoined welly-boots). A few years ago I interviewed Sally James for a radio special (still available online, by request

) and she remembered the welly-phone, but neither of us could remember why they used it!! No doubt though it was for the usual competition entries... questions to guests... etc... although it was all-but-entirely dropped by the time of the supposed 'classic' period (1979 onwards).
So, Tiswas was on-air with phones for almost 3 years before Swap Shop, but not across the whole country. Indeed Tiswas was never networked, here's the list of how it spread around the regions:
http://www.tiswasonline.com/look_in.php?details=off
(full episode guide:
http://tiswasonline.com/episode_guide.php )
All that said, The Golden Shot pipped the lot with the phones!!