The more we demand our smartphones do, the more on-board storage they need.
As cameras get bigger and better quality, image files increase. Music playback is now standard, so we need somewhere to put the music files. Many devices still remember when "smartphone" meant being able to edit documents, and we still need somewhere to put them. Podcasts. Ebook readers. High quality video playback. Extra applications (more of a problem on platforms that don't have any to begin with). The list goes on.
And then there's the simple fact of operating systems getting bigger and bigger, and needing somewhere to put all the system files.
Once upon a time, "extra space" meant having a memory card slot. Then someone had the bright idea of soldering a memory card to the motherboard, and hey presto, on-board storage.
Most devices have both for added flexibility, although some of them make it a painful business getting at the removable card - under the battery cover or, in some particularly stupid cases, under the battery. Some only have the on-board storage.
And then there's Windows Phone 7 which, apparently, won't have a card in any device.
I don't care about Windows - there are many other and much better reasons why I won't have anything to do with it - but it doesn't make me very happy when other people decide to save themselves a buck by cutting that off the feature list.
Here are the reasons I will never, if I can at all help it, own a device without:
Let's face it, nobody's encouraging you to buy a phone and keep it for two years, even though that's how long plans generally last. Some devices aren't even supported properly past one year. So being able to take all of the files you want with you from one device to the next easily is nice, even if you're not a reviewer who has to do it several times a week (I'm not, sadly, I just manage to sound like it). Some people, of course, may be tempted to point out that nowadays we can do that easily with desktop software and syncing, which brings me to my next point:
Having removable storage means I'm not tied to someone else's - frequently quite bad - idea of how I should manage my own files. I use Linux on my desktop computer, so I can't run most desktop "companion" software anyway, making it specially important for me to not have to care. Microsoft have announced that Windows Phone 7 will only talk to their Zune desktop software, which is one of the very good reasons they can take their software and shove it. Apple devices only want to talk to iTunes, although there are workarounds. That sort of arse-hattery is one reason I still haven't considered buying an iPhone or iPod, even if I wanted to pay their exorbitantly inflated prices. I was bitten by buying a digital audio recorder that relied upon companion software which, surprise surprise, doesn't run on Linux. And even if you are happy using Ovi suite, or iTunes, or Zune, what if you buy a different platform? Ovi Suite will only talk to Symbian, I'm not sure about iTunes but I'm pretty sure Zune won't be happy talking to iOS or Android or Symbian or Bada or... Nokia have gone down a fairly sane route - their on-board memory is generally accessible via USB Mass Storage, the same way USB memory sticks and cards plugged into card readers are - but even then you are relying upon the phone working.
What if the device breaks?
I managed to kill my N97 mini by leaving it on the roof of a car. My anguished scream is still echoing around the multiverse. Considering the interesting shape the phone was in after it was run over, I was amazed to find the SIM card and memory card unharmed. I could simply plug them back into my ancient N95, resync my calendar and contacts with Google, and away we go - images and ebooks and podcast downloads all intact. My alternative would have been to go to a repair centre, wait an indeterminate length of time and pay someone for the privilege. No thanks.
With 32GB of on-board storage appearing routinely now, this is almost a non-issue. But, what the hell, why not say it: If the on-board disk dies or fills up, having a replaceable, upgradeable extra is not to be sneezed at.
You may not have noticed, but some software demands memory cards, or comes on memory cards. Some GPS software companies will send you a card containing available maps. If you install a mapping program that can store maps locally (and if you don't, you're relying far too much upon network coverage), they will often warn against storing maps on a built-in drive.
As a final, bonus point: I don't trust the bastards.
You can make up your own minds, but I know which way my wallet will be voting.