My new Samsung Galaxy S3 phone takes a micro-SIM (see the Wikipedia page about Subscriber Identity Modules for details ). All my other mobile devices take a mini-SIM so I can’t just put the SIM from my old phone in my new phone. I’ve just made my second application to Virgin Mobile for a new micro-SIM, the first time they sent me a nano-SIM by mistake. Also if my new phone breaks I will have difficulty in getting a micro-SIM to run in a mini-SIM device (it should be possible, but will be difficult at least). I may even have to ask my Telco to send me a new mini-SIM to allow the use of an older phone if my Galaxy S3 breaks.
The difference between micro and mini SIMs is 25*15mm vs 15*12mm. For a phone with a 4.8″ display this doesn’t seem to be a great benefit. It doesn’t seem that the phone would be much bigger if they had designed it for a mini-SIM. If they had used a nano-SIM which is 0.09mm thinner that might have allowed them to make the entire phone thinner, I think that such thin phones are a bad idea but the reviewers seem to like thin phones with small batteries. I think that any device which is large enough to have a speaker somewhere near my ear and a microphone somewhere near my mouth will be big enough to fit a 25mm long SIM card.
It seems to have been a trend in Australia in the last few years towards only selling unlocked phones on contracts (relying on the contract terms to lock the customer in) and only use locked phones for discount sales for pre-paid use. Also the “free” phones in Australia are considerably more expensive than buying a phone outright . So I’m sure that most people have a collection of older phones which in future can’t be easily interchanged with new phones due to SIM card size differences.
This is more of a problem due to the fact that modern phones seem to have a low quality of hardware production, the majority of Android phones owned by my relatives have failed in some substantial way well within the two year replacement period. I don’t believe that I can rely on my Galaxy S3 working until I want to buy something better, I expect that my old Galaxy S (which has a hardware fault that makes it crash regularly but is mostly usable) will be pressed into service again.
In terms of phone purchases, buying a phone that takes a micro-SIM seems like a bad strategy as there is an even smaller nano-SIM available. For all I know Samsung will release a Galaxy S4 or Note3 that uses a nano-SIM and give me the same upgrade problem in a couple of years time.
I wish that the people who reviewed phones would pay more attention to the real world use cases than to slightly better specifications. The micro and nano SIMs seem to provide no real benefit for users. Saving a fraction of a gram in device mass or a fraction of a millimeter in one dimension might seem nice when aggregated with other small savings, but for the user it’s no real benefit. Being able to interchange a bunch of random phones is a real benefit. It’s also a real benefit to be able to buy a phone and expect it to just work immediately. With the current state of the market one can’t buy a phone and make any assumptions about the SIM size that it will accept, at best this requires some extra research before buying and at worst this could involve some time without phone service.
I think that a major feature for a review of an important device like a modern smart phone should be how quickly and easily it can be deployed for full use. When SIM size issues prevent a new device from being used properly for over a week (as has happened for me) then it seems like a design failure.
-  http://en.wikipedia.org/wiki/Subscriber_identity_module
-  http://etbe.coker.com.au/2012/09/22/phone-prices-australia/