In its heyday Windows Mobile was the OS of choice for the disabled user, due to the open access to the OS by 3rd party developers, allowing the easy creation of screen readers for example. There were also great support for hardware keyboards, which also assisted those with visual problems.
Windows Phone 7 is a much less accessible OS in more ways than one, as noted in this document by One Voice, an organization dealing with accessibility in IT.
Despite Microsoft Windows for PCs and laptops offering a range of built-in accessibility features, the current version of its smartphone operating system â€“ Windows Phone 7 (formerly called Windows Mobile), a cut-down version of the familiar Windows for PCs â€“ is not considered to be very accessible. It does not have a built-in screen-reader, and it is not constructed to allow others to write apps accessing the screen elements.
They do however go on to say that the situation is set to change with Windows Phone 8:
However Microsoft is working with disability charities worldwide to develop a broad range of accessibility features for Windows Phone 8, which is set to mark a major new direction when it appears later this year.
Accessibility features in iOS 5 include VoiceOver, which will read onscreen buttons out loud before activating them with a double tap, Large Text, Zoom and other features.
I suspect even those of us who do not have a hearing or visual disability would not mind having their web pages read to them or being able to make the UI larger for in-car use, so hopefully Microsoft will in fact deliver.