Cellular models of the new iPad Air 2 and the iPad mini 3 models come with the Apple SIM card rather than a SIM card from a particular carrier. This is a great move by Apple to both reduce the number of specific models that we have to carry and to make it more convenient for customers to move from one carrier to another or activate service when they travel outside of the country.
Verizon customers who are not on a GSM network like AT&T, T-Mobile or others will have to go to the Verizon or Apple store to get a Verizon SIM to replace the Apple card. It was also revealed this week that if you sign up for AT&T service for your iPad that AT&T will lock your SIM card to their network. This sort of defeats the purpose of the Apple SIM card, however, Apple will sell you a spare Apple SIM to replace that locked card should you want to change carriers.
While the participating carriers are somewhat limited now, AT&T, Sprint or T-Mobile in the USA or Everything Everywhere in the UK, the convenience of choosing a carrier and plan right from your iPad is compelling. Since most of these carriers offer short-term data plans you can choose the length of time and plan according to where you are. I assume Apple will expand the number of international carriers and this will be big help for international travel.
Even without the Apple SIM, if you are traveling internationally or into an area where service is better than your home carrier and plan to be there awhile, you should consider contacting that local carrier to get a SIM for your iPad that works with their network. It can save you a bunch in roaming charges!
I would love to see this same convenience carried over to the iPhone, however, since most of the iPhone sales are still based upon a carrier subsidized contract basis that is unlikely for some time. I do believe that ultimately the carrier subsidized model may become less popular it does have a strong legacy.
Removing the SIM from your iPad is a simple process. Your iPad came with a SIM eject tool which is basically a paperclip with an end that will fit into the release hole on the side of your iPad. The SIM is contained in a small tray.