Complex sentence: O2 began trials of NFC technology in, with 500 individuals taking part using a selection of Nokia handsets to make payments at selected retailers, and travel the London Underground with transactions made via Barclays.
Split into simpler sentences: O2 began trials of NFC technology in, with 500 individuals participating in the trial. The individuals used a selection of Nokia handset to make payments at selected retailers, and travel the London Underground with transactions made via Barclays.