You may be right.
Quote:The iPhone 3G automatically switches between 3G and 2G networks for voice and data connections. In theory, the phone should hop off 3G when signal strength is too low or non-existent, and hop back on when the signal gets better. In our experience, however, the iPhone 3G isn't aggressive enough regarding the switch from 3G to 2G. In other words, you may find that your phone stays connected to a 3G network when the signal strength is too low to allow incoming or outgoing calls.The simple solution is to manually turn 3G connectivity, forcing a switch to 2G -- which may take several seconds -- and likely a boost in signal strength.*
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More?Boosting iPhone 3G signal strength http://reviews.cnet.com/8301-19512_7-10115619-233.html