Nokia 3210
Snake, changeable covers, and a week of battery life.
The first phone that was genuinely a mass-market object rather than a business tool, with an internal aerial and a game everyone played.
Texting was invented socially on this phone. T9 predictive text, the 160-character limit, and the specific rhythm of pressing 7 four times for an S.
It was indestructible. Dropped on concrete, the battery flew off, you clipped it back on and carried on.
Cost back then
£150, or free on contract
Goes for now
£40–£120 working