This quick post was inspired by a comment the previous blog entry about 3G security. As the comment mentioned, 3G security procedures are just used if the SIM card, which should actually be called a UICC (Universal Integrated Circuit Card) these days, contains a USIM (Universal Subscriber Identity Module), i.e. a folder branch and internal logic for 3G security. For details see here.
As also mentioned in the comment, many network operators allow the use of old 2G SIMs (i.e. UICCs with a GSM SIM folder) in their 3G networks. From the outside, a UICC with a 2G SIM and a UICC with a 3G USIM can't be told apart unless the operator has printed something on the SIM that hints its a 3G SIM card. In practice, it's even worse as many network operators still sell 2G UICCs today, probably because they are a couple of cents cheaper.
But this approach now backfires with LTE. Here, the 3GPP specification explicitly states that 2G UICCs can't be used. And indeed, when a user has a 2G SIM card (which he might just have bought recently) he won't be able to use LTE because either the mobile won't even try or because the network rejects the user. I've given it a try and it really doesn't work.
In other words, those network operators on the cheap side will have to exchange a lot of UICCs in the future when they go live with LTE and their customers with an LTE capable device will be stuck in 3G.
Yes, nothing new here. On the contrary if you buy a new LTE phone or iPad – you will be normally supplied with necessary SIM card to be able to work with LTE.
Also iPhone 5 and 5s as well as iPad Air and other devices, have a new sim card standarts, like nano SIM, so you previous sim has to be changed anyway. It is not of a big deal in my opinion…
I somehow managed to keep a SIM on the go since 2005 or so, which was just before 3G SIMs were sold by my operator as standard – I recently got a company phone with LTE support, and after a few weeks of us got around to getting an LTE capable SIM so as to use the LTE network for data! – Although to be honest, the HSPA+ DC network was giving fast enough data rates, especially as the local LTE network is pretty full with all the other employees using the LTE network on their company phone too!