Nana, maybe he is really busy. And maybe he has no money left on his phone...
This like that really happen. You know once I was in much the same situation, but I had to wait for 2 weeks. I thought I would go crazy! I started calling his friends but I couldn't reach anyone! Finally I found out that he had just gone to some place for business and his phone (and tall the phone numbers including mine saved in it) was stolen. So, it was like this.
I hope your bf calls you soon.