I am traveling to Europe next month, and I am looking for some good London and Paris maps for my 3G. Can someone tell me if the Frommers apps have detailed maps for these 2 cities? I am trying to avoid AT&T's expensive data roaming fees, because I imagine using GPS+Google maps would download load a lot of data. Does anybody have any experience with the Frommers maps or maps from another travel app? Can I cache the Google maps on my phone? Are there any worldwide GSM SIMs that have reasonable data rates (I have an officially unlocked 3G iPhone)?