Surprisingly enough, Seesmic, or more accurately, Luic Le Meur, one of the founders, responded:
So, what are the keys to delivering bad news?
Put yourself in the customer’s shoes. Does the company really think anybody will pay their carrier the penalties associated with changing devices or switching carriers just to use their iPhone or Android product? All this message does is annoy its audience – exactly those that the company wants to keep.
Offer valid alternatives that do not require much effort or expense. In this case the company could have just as easily recommend the native twitter and facebook applications for the BlackBerry. It would have made a positive message that could have gained added goodwill.
Postscript: In the time since, Seesmic updated the original blog post, well done!