Do you reboot your phone when it drops a call?
I can't think of a time I've had a dropped call since getting my iPhone. I have rebooted a few times when Safari got a little unstable, strangely always on FreeRepublic. After a while it doesn't like the links to articles or specific replies except that the link to Reply 1 always works. I reboot the iPhone and the links work as expected for several hours then go hinky again. I've reported the bug to Apple. I think it has something to do with the auto opening of a new window that FR does. No other site causes this specific problem.