Well I have tried on and off to download the WLM and am always told that my 8310 is not compatible. Today I look down at my screen and there is the Windows Live Messenger icon. I click on it and log on and everything works. Not sure how it showed up but I am not complaining.
I finally got WLM after a few tries. You definately dont need OS 4.5 to get WLM. Just keep trying again and again and it eventually goes through! i switched my data plan from $30-300mb to $30-6g and i had no probs whatsoever with the msger. I just had a slight prob with my browser though....i got a http 500 error or something and all i did was switch the emulation mode and did a battery pull.....but ya battery pull usually helps lol.
it worked fine for me on the $15 unlimited email plan. When i moved over to the $30/300mb plan - it stopped working. I reinstalled the app from the link on the blackberry page, and voila! it's working again.