The "black screen" is the display "timing-out" to conserve battery, you can always change that by going into settings and navigating to the display settings. As for the dropped calls, that's odd, I had the Vibrant for about a month and I didn't stop calls. You might be in an area with alot of "dead" spots maybe. If problems persist, take it back to T-Mobile and you should not have a problem getting a new replacement unit. Fyi, the Vibrant does suffer from inaccurate signal readings, don't be misled if you see only 1 bar, just add 2 bars to what you see and that should be closer to accurate. Samsung has acknowledged this and will send out a fix in the near future.
Linear Mode
