Users continue to report poor 3G signal strength under iPhone OS 2.1. To be clear, iPhone OS 2.1 does not purport to actually boost signal strength. Instead, it provides "more accurate" signal strength display, which, in most cases, means more bar bars, but not necessarily better reception or ability to make/receive cals.
Two sample reports from this Apple Discussion thread:"the point is that the 3G did go from zero to all the bars but still dropping the calls! "I just bought my iphone yesterday and asoon as i got home the reception … Read more