Buying apps for your smartphone ties you to the operating system in a similar way to camera lenses for a particular SLR system. With Windows Phone struggling to compete with iOS and Android, Microsoft needs more incentives to entice users to switch.
Back in the day, people thought nothing of upgrading their handset at the end of a mobile phone contract. Typically, the operator would offer a selection of phones that would be free if you took out another year-long contact and you either picked the best or tried to negotiate to get something a little costlier included in the deal.
Few people were loyal to a certain brand or operating system - it hardly mattered whether you had a Nokia handset running Symbian or a Sony Ericsson running Java - they all had pretty much the same limited functions.
Switching handsets involved little more than swapping over the SIM card and importing your contacts into the new phone's memory. Then you scrolled through the new ringtones, picked one and you were good to go.
These days things are a lot more complicated. Not only do we all store a lot more information on our smartphones, but we're also tied into the operating system by all the apps we use on a daily basis. From the latest version of Angry Birds to essential commuting tools such as UK Train Times, these apps become almost a minimum requirement when we're choosing a new phone.
There's certainly some crossover between Google Play and Apple's App Store, so it's possible to switch between Android and iOS relatively painlessly. However, you'll still have to buy the same apps again as your licence for Android apps doesn't entitle you install the iOS version.
This is a pretty big disincentive for some, and it's an even tougher ask to switch from either Android or iOS to Windows Phone. Nokia is one company pinning its future on Microsoft's OS, but while Windows Phone is a veritable rival to the Big Two, there's the problem of apps.
Developers tend to release an iOS app first, then Android and might then consider Windows Phone. It's never Windows Phone first. The availability of top-tier apps is getting better, with Facebook, Twitter, eBay, Amazon and Skype all present and correct in the Windows Marketplace. They still need to improve in quality - the Twitter app has an average rating of 2.5 stars - but things are moving in the right direction.
How to get more people to buy a Windows Phone, though? Not only is there little incentive for developers to produce Windows Phone apps, there's nothing to persuade the average punter to opt for a Lumia 900 over the Samsung Galaxy S III or iPhone 4S as all cost roughly the same over a 24-month contract.
It's harder, of course, to tempt existing Android or iPhone owners who will have to forfeit all their paid-for apps. Well, here's an idea Microsoft: why not offer those users a rebate to cover re-purchasing all those apps in the Windows Marketplace, and perhaps a few extras as well? That might just be enough of a draw for people to make the switch.
With the next version of Windows Phone - Apollo - just around the corner, we have high hopes it will rival iOS 6 and Ice Cream Sandwich. However, until there's more of an incentive to commit to Windows Phone it won't cause Google and Apple to lose much sleep.
UPDATE: 11th June. Thanks to Calum, who tweeted to point out that Carphone Warehouse is offering a £40 app voucher when you buy a Lumia 800 or 900. Plus, you also get a free pair of Monster headphones (Nokia Purity HD). To get the voucher, head to nokiafreeapps.com and enter your details (including IMEI) within 14 days of buying the phone. Note that you'll need to have purchased your handset from Carphone Warehouse - the site won't accept IMEI numbers of handsets from other shops.
It's a decent offer, not least because the Lumia 800 is available from only £20.50 per month with no upfront cost. However, for us, it's still the absence of apps such as UK Train Times and others which we use on a daily basis that prevent us from ditching our iPhones and Android handsets and switching to Windows Phone.