I'd try calling a few more times.
I've had a similar (thought not quite as lengthy) experience where I couldn't reach a customer for several weeks, ultimately turning into a few months of hanging onto a knife. I finally left two or three messages on his voicemail, facebook, youtube, and any other form of contact I could find and told him that he had another week before the knives went to other buyers. He called me shortly after the ultimatum and apologized for his absence and lack of response. Turns out he had been in the hospital for a while and had a few more pressing matters to attend to. Ultimately, he backed out of the deal due to recent financial developments, and I sold the knives to other buyers.
In your case, you of course always have the option of hanging on to it for a bit longer, or selling it and making him another if he eventually gets back to you after the fact. As long as you make repeated attempts to contact him, I'd say he will probably understand whatever decision you make.
In today's world, it seems that nearly everybody has at least 3 or 4 ways to be contacted (phone, email, facebook, linkedin, PMs on forums, etc....)
With smartphones, tablets, and personal computers, there's very few reasons that a person can't stay in touch or send a quick message. Try whatever avenues you can find, give it a few more days, and then do as you see fit.