If every episode of Eureka this season is like this one, it's going to be a great summer!
What I liked the most about this episode was that the characters actually acted like themselves, while still retaining the character developments they've had. Specifically, Jo was still the action hero but maintained the emotional growth as a person she's experienced. Similarly, Fargo is still the comic relief but retained the intelligence and confidence he seemed to pick up. I also liked the return to sexy and intelligent Allison, coupled with the confident leader.
One thing I would have liked a callback to was Henry/Carter changing history the first time. Henry at least could have had a throwaway line about the butterfly effect not being as bad as it seems.
My assumption is that Carter (kind of) didn't forget the phone, but that JC's character tricked it from him when they switched coats.
Also, I don't get Carter's reluctance to leave Allison and... what, assault the guards at the dance? At least stick around to see if the phone works before going on a death charge. It wasn't like he was going to make it back to the bunker in time anyway.