A change in the MobileMe preference panel hints that Apple may be planning to release a free version of service, according to 9to5Mac.
Notice in the screenshot below that the account type of this user is listed as "Full Member". Perhaps Apple will announce that a Free Membership is coming in the near future?
This is because MobileMe currently has different types, as someone pointed out you have a trial but also for a family you get a full member then different sub members off the main account.
I suspect it will just post options such as Full Member and Trial Member. I would be surprised as it hasn't popped up on other sites as well regarding a free MobileMe option happening.