Nokia exist now as a cautionary tale to the likes to Google (and by extension Samsung), and of course to Apple. Cast your mind back ~10 years, and the Nokia 3310 and 6210 were simply the mobiles you bought. Why? They were well built, easy to use and everyone knew that Nokia were at the top of their game.
What went wrong? With hindsight, it seems they just utterly failed to build on their good brand and reputation. They started facing some competition from Motorola and a few others who offered (imho) poorer UI's, but better looking hardware. And I think that is the key part - Nokia not only failed to keep ahead of the curve design-wise, they seemed to completely miss the shift in what people wanted. Good solid hardware and features, with good battery, were no longer enough. Mobiles became a fashion accessory, and the likes of the Razr offered far more interesting designs than the Nokia bricks. Oh sure, there were snap-on cases for Nokia phones, but they didn't cut the mustard for long.
They had the potential to get ahead of the curve again with the N-Gage. It could have found a solid niche for itself, but some bizarre usability choices (holding it sideways to make a call, so you look like a buffoon?) killed it on arrival. While they flapped around on this and continued to fail to deliver what people actually wanted, Apple (and others) continued to eat into their market share. Nokia seemed to completely fail to see the touchscreen/smartphone tsunami.
It's a sad tale, but as I said at the outset, every manufacturer should study Nokia's downfall to help mitigate their own demise.
Order and simplification are the first steps toward mastery of a subject -- the actual enemy is the unknown. -- Thomas Mann