Unless I'm mistaken, but I'm pretty sure I'm not, you need six years of service to be an unrestricted free agent.
Guys like Johnny Jolly, Daryn Colledge, Nick Collins, Tramon Williams, Jason Spitz, Atari Bigby, and Will Blackmon will all be restricted free agents.
Meaning Green Bay will have an option of tendering them which means that if signed to an offer sheet with another team, GB can match the offer or receive compensation depending on the tender. Since it'll be an uncapped year and the Packers have a lot of money to spend, they'll likely put high tenders on key players such as Collins, Jolly, Bigby, Colledge, Spitz, and Williams. It'll be unlikely anyone gives up high picks for any of those players in this year's draft which is deep.
The unrestricted free agent list is basically this
Chad Clifton
Ryan Pickett
Aaron Kampman
Brandon Chiller
Those four will be able to sign anywhere, but I certainly see GB using the franchise tag on Kampman and they'll get a transition tag to use as well which I would use on Pickett.