I think that riku keyblader was right about this particular event in the story.
The first time it happened he was obviously afraid of exactly what was going on and thus attempted to call his friends for some form of reassurance.
The second time however, some strange things had already happened and he would of course begin to wonder what was going on. He was attempting to hold on to something that he believed to be real, and thus called to those that he felt that he could trust.
Another thought could be that he did not remember any of the people that could move when the city froze. He was the only one that was aware of what was going on, and afterwards nobody else remembered what had happened. He would have been looking to see if there was someone else there for him rather than being alone.
I never really gave this any thought before, but this is what I came up with just now.