Registered today just to post my results...
Wife and I both received our phones yesterday. Both exhibited the issue straight away, repeatable every time, and we live in an area with strong 3G coverage.
Last night, decided to try the sim trick. I simply removed it, and replaced it, and immediately could NOT repeat the signal drop issue. I did this with both phones, and they both haven't exhibited the problem since.
Just wanted to throw my experience in the "pile".