Nokia 110 4G Black (Unlocked) (Dual Sim)

It comes with a £10 Vodafone sim, but you can use your own sim card instead which is what I've done.

The product page says it's for use with Vodafone, though you can read on Questions & Answers that Argos says it's unlocked and I've tested it, too. With 2G (2033) and 3G (2023) on their way out, I decided to buy this one as it's 4G.

Argos is selling this for a decent price from what I've seen while others are charging £25-30 or even £40. If they actually sell it, who knows.