Users posted their issues in a Samsung Community thread entitled "Note Freezing and unresponsive". While some users suggested it might be due to carrier modification issues, others from various places using different carriers also reported problems.
The main culprit seems to be the Contacts app, which is unfortunate considering how vital that app is for calls, messaging and other communication.
As of now, Samsung hasn't issued a statement on the issue. Users have resorted to frequent hard resets, factory resets and not installing third-party apps, but the problem has persisted for some.
It sounds like this is a software issue and Samsung will probably issue an update. But considering the company does tend to take its time when it comes to updates, affected users might have a wait ahead of them.