As RIM announced that the PlayBook will be able to run Android Apps, the competition will be very interesting.
Additional factors need to be considered.
Things like malware, adware, and so on for all these OS. As more and more people get mobile devices with these OS, depending on how all these players in the market protect their OS and devices against this type of security issues, the consumer will go for what works and do not need all the anti-virus *************.
Other rumors like carrier independence, if it flies, and Apple successfully bat a hit with this, the consumers will go where their money is worth every penny.
Making your own hardware has been a key for Apple success. Maybe RIm enjoyed some of it, but most of all the other OS are so fragmented in terms of hardware, that for them it is not easy to maintain, release, as it is difficult for any IT department to support them.
So the distinction between enterprise/business and regular customers will also show a different distribution of the market share.
The iPhone will get stronger. The rest would fall into the 'el cheapo' phone category. Not price related, but quality and performance.
And believe me, I've been strongly considering getting an Android phone on t-Mobile to maintain my unlimited plan with tethering, but so far, none of the phones I have seen do really catch my attention.