I picked some up this past saturday, forgot that I left it in the garage overnight when I went out to plow... only to come home in the morning to find the packs partially frozen.
Brought it inside, smacked the packs, left it out on the kitchen countertop, took a nap.
Woke up, noticed some swelling, proceeded with the brew-day-sunday as planned. By the end brew session, packs were (almost) fully swelled.. pitched as usual. All fermenters were perking away the next morning, and going crazy on day 2 as they should.
Just let it warm up slowly at room temperature, smack the pack, shake.. wait.. shake some more.. If it swells up you/re good to go.
And yes, do a starter if you can - especially if its a bigger beer >1.060 for peace of mind of a healthy and quick fermentation. I would have done one, but didn't want to wait until the next weekend to brew. Still worked like a champ.