Quite a few mobile devices come with a SIM card. It’s not a memory card, although the thing does have a few memory-card-like features. Still, it’s nothing to get excited about.

Before anything, the obvious answer to your looming question: SIM stands for Subscriber Identity Module. It’s basically an ID card used by a cellular device. It uniquely identifies the device to the network. You need an activated SIM card to access mobile data.

The original idea behind the SIM was that you could upgrade your phone service simply by purchasing a new mobile device and installing the old phone’s SIM. I don’t belive that idea ever came to fruition anywhere.

In fact, the whole SIM upgrade thing reminds me of the old processor upgrades that manufacturer’s once offered for PCs: You could pay extra and get a computer with an “upgradable processor.” The problem? The new processor (a single chip) often cost more than an entire new computer.

A lot more.

Not only that, the next generation processor that was faster, better, and cheaper didn’t fit into the old computer’s processor slot. The upgradable processor idea fizzled.

Ditto for the upgradable SIM: I’ve never yet had a new phone that would accept a transfer of my old phone’s SIM. Nope, the new SIM is a micro-SIM or a mini-SIM or maybe a next generation 4G SIM. It just never worked.

Tangential to the upgrade issue — call it a selling point of the SIM — was that you can store your phone’s address book on the thing. That feature is still an option on many phones, but I recommend against it.

While the SIM can hold phone numbers — an address book of sorts — the memory capacity isn’t that great. Not only that, the purpose for storing the numbers is so that you can easily transfer that information to your new phone. And, of course, you can’t that. Or you could try, but it probably won’t work. So storing an address book on a SIM is pointless.

So can you use a SIM to store data?

Hardly. Even if you could, the typical SIM has a maximum of maybe 8KB of storage. Or, if you could access it, 64KB of flash storage. Keep in mind that even the cheapest smartphone has 8GB of storage, which is one million times the storage available on a SIM.

So you can flatly rule out using a SIM for anything other than its basic purpose, to identify your mobile device to the cellular network. If you want to store files, get a MicroSD card. And if you need to transfer files, you can set up a transfer as described in any of my For Dummies mobile technology books, or you can use an app like DropBox to shuttle files between computers, laptops, tablets, and cell phones. It’s a better solution that using the SIM, any day of the week.