( I will refer the Mini Sim as Sim itself, since its standard universally)
Most of the latest Nokia Device come with a Micro Sim slot nowadays. I'll talk about the global scenario regarding this.
Traditionally, the Western mobile cellular networks like US, UK and European nations, usually have subscriptions with the Mobile device, some ties they tie-up with Mobile producing Companies. Since there are many tie-ups between major network carriers and Mobile manufacturers, the end user gets support for both, the micro Sim card and the usual sized Sim cards. However, this might not be the case everywhere
Now Cut back to growing Mass Consumption and growing markets like India and other Asian nations, there are no tie-ups between networks and Mobile Manufacturers, whatsoever.
Unlike western markets, most of the phones available are unlocked and not linked to any networks; since they are a wide array options for network carriers, Mobile Sim cards are easily available; and one can own countless Sim cards from different mobile networks (theoretical possible but practically unfeasible). Moreover, those Sim cards are mostly bought from small shops and outlets on the streets than the Network Carriers Shop.
But there is a work around for this, there are Sim cutters but once you cut short the Sim; you cant get it back, so there are micro Sim adapters which enlarges it the micro Sim without affecting the card's dimensions. Also, one can replace the Sim to micro Sim or vice verse but the user can use only one Sim at any moment, Most Network carriers don't allow duplicate Sims.
The transition of the Sim to micro Sims, would be the same like SD, mini SD cards; to the micro SD cards. The problem is, not all future devices use micro Sim, so for now, the mobile devices that use micro Sim are premium phones, so the end user can afford/take the irritation of toying between both Sim card types.
