When I was in the store getting mine they were talking about how they'd been having allot of issues activating phone because of the large demand was causing a backup in the switch. There was a guy that walked in about 5 min before me and his would not activate, but then mine activated perfectly. So I guess it was intermittent. Makes me wonder if you got caught up in that backup when you activated the second sim.
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BB Bold --> Droid 2 --> HTC Thunderbolt