Shares of Research In Motion have declined from $148 to $60 in four months, falling along with most tech stocks. The difference between RIM and, say, Yahoo? Microsoft still wants to buy RIM, say some analysts cited by Reuters . Forget Google's still-not-on-the-market Android phones; RIM's BlackBerry is the only real competition for Apple's iPhone.Like Apple, RIM offers not just the hardware but the software and services that run on top of it; RIM does Apple one better by also selling back-end servers that companies install to manage their workers' email. Microsoft is in that same business, but it's not as good as tying everything together as RIM is. The speculation is that RIM shares would have to drop to $40 or so, at which point Microsoft might bid $50 a share, or $28 billion for the company. This much is not speculation: RIM would be a better buy than Yahoo.