Old smart phones (Earlham NR4)

We're looking for old smart phones which are unlocked and we can use in a theatre production to transfer audio through to each member of the audience.
It's an integral part of our show but we can't afford to hire headsets for each show so we're looking for an affordable alternative.
The phone just needs to be able to wifi - unlock with a headphone jack.
Obviously we're not asking anything that is worth money.

Thanks so much.