Iphone 4 failed to make outgoing calls

My new iphone 4 failed to make outgoing calls for about 80% of the time. Incoming calls are good. Switching airplane mode on-off-on will work again. Also Switching 3G on-off-on will work. So far, it only happens to my home area and suspect it is the specific cellular tower near me.
I reset my iphone 4 network setting but it does not help. I also changed sim card and it doesn't work neither.
However, my old iphone 3G does not have this problem at all.
In order to check if it is the defect of my iphone 4 only, I borrowed my friend's iphone 4 and tried. As demonstrated in this video, Both iphone 4 failed to make calls.
Both iphone 4 works good at my work place and other place I visited. It towards the conclusion that the problem is the interaction between iphone 4 and a particular cellular tower. I have requested AT&T to check the tower near by my home which is around the northbound of Evergreen College, San Jose, CA 95135. Hopefully, they will identify the problem.