How long would you wait for your boyfriend . . . ?

My BF of 4 months left for 3-wk business trip last weekend. We're supposed to meet for 3-day getaway at end of his trip. Spent night b4 together and I took him to the airport the next day. He was kind and friendly, but phsycailly and emotionally disengaged from me. Our goodbye was a perfunctory peck and hug. Left him a sweet vmail saying hope he arrived ok, a little concerned, you seemed disengaged, can we talk before our trip, please call. He responded by text saying that he got the vmail & will call. That was 8 days ago. Haven't heard from him since. How much time should I give him to fulfill his promise to call before I should question his integrity and commitment to the relationship?