The iPhone and Android phones are pecking away at BlackBerry market share like vultures on roadkill, especially within the walls of the enterprise.

New BlackBerry phones and an improved BlackBerry OS 7, along with a promising, consolidated platform in BBX, and even an Apple-esque leak about a new phone (code-named London) are not enough to satiate end users lured by new mobile apps, and swayed by a massive cultural shift. Even Windows Phone 7 is gaining some momentum, thanks to a compelling user experience and a healthy and growing list of apps.

Corporate IT is finally changing its stance on a BlackBerry-centric mobile world. Or as InformationWeek's Eric Zeman recently proclaimed: "iPhone Ousts BlackBerry From Boardroom, iPass Says."

It's time, therefore, to take a closer look at the contenders to replace the BlackBerry. For several weeks, I've been testing the iPhone 4S (AT&T), Google's Android (Gingerbread version) running on a Samsung Galaxy SII (a T-Mobile version and one from AT&T,) and Windows Phone 7.5 running on an HTC Radar 4G (T-Mobile) and the Nokia Lumia 800 (not available in the U.S. yet).

iPhone 4S

I tried to truly use each phone on a daily basis, rather than spend my time pouring over specs and trying every feature. In other words, this comparison focuses on the usability and practicality of each platform. In fact, there are many useful features that I found and couldn't find room for in this comparison. I hope readers will share some in our comments section as well.

I am, in fact, a BlackBerry user through and through. I've been using one for the past several years, occasionally testing some of the other platforms. I've recently switched my full-time smartphone allegiance to the iPhone 4S, thanks to a loosening of corporate IT policy at InformationWeek's parent company, TechWeb.

I tried my best to mimic phone experiences across all platforms. That's a bit harder than it would seem, given that many of the underlying services--notifications, location-based services, social network integration, and so on--differ. I set them all up to use WiFi, GPS, mobile networks, and a common set of applications.

Smartphone choice comes down to a handful of items: design, overall user experience, applications available, enterprise support and security, and a grab-bag of other features--including camera, cloud services, voice-activated services, and performance issues such as browser speed.

There's one more thing: Some buyers care greatly about notions of openness--the ability to run whatever apps they want, to use a phone on any network, to customize the phone without limitation. Other buyers just want the most simple, flawless experience, and don't wish to deviate from the pre-set choices. Neither is wrong, it's just a personal decision; and truth be told, some people don't even know that it's a choice they can make.

In this regard, Apple and Google sit on opposite ends of the spectrum, one controlling everything from the phone to the OS to the apps (Apple), with the other creating a somewhat-open OS that runs on many phones with a fairly accessible application ecosystem (Google). Microsoft sits somewhere in between, choosing not to manufacture phones (for now), but creating fairly tight rules about the hardware its OS runs on.

These are difficult decisions, especially since most people need to live with the choice for two years (the length of most standard carrier contracts); within those two years, everything changes again in dramatic fashion.

You can't go wrong with any of these platforms, from an end user point of view. I chose the iPhone for now because it marries my personal and professional worlds in ways that no other platform can quite match. But Android is damn close, and with Ice Cream Sandwich (Android 4.0), it may indeed overtake iOS. In fact, if the Samsung Galaxy Nexus is an even better version of the Samsung Galaxy SII, I may wish I had waited to make my final choice. And in another year, as Nokia and other manufacturers keep making better hardware for Windows Phone 7, and as Microsoft continues to improve its OS with the Apollo release, I may regret my choice yet again.

But such is the way with the mobile wars.