This happened to me on my first storm. I had made calls on it all day and then all of a sudden I started having problems with the other person hearing me and then the phone would tell me the call was lost. Eventually it quit having this problem after I called *228 then hit option 2 to update the phone. Also under Manage connections -> Mobile Network Options -> Network Technology, I switched this to 1XEV instead of global.
I had the same issue late Sunday. It was to a land line as well then we switched to a verizon-verizon call. Still happened. I attempted to send a txt during this period and it wasn't delivered and returned with a network error. Seems like there was a giant network problem ATT.
In 4 weeks with the Storm, zero dropped calls. If you keep dropping calls, I'd give VZW a call. Could be a hardware issue with your unit. With all the other bugs I've seen reported here, anything's possible. Or as a PP suggested, dial *228. Instead of #2 to updating roaming, do #1 to reprogram.
In no way am I loving everything about Verizon, but coverage is not one of there problems. I have been on almost every major carrier and have had by far the fewest reception issues with them. Not a single drop since I've had the Storm. Maybe it is where you were or live.