Quite a few people are posting on the internet that they are having problems with holding their iPhone 4 and losing signal. I have experienced this too and it isn't just something that happens occasionally, it actually happens each and every time I hold my iPhone 4.
The problem essentially is to do with the part of the antenna around the black bar on the bottom left of the phone. If your hand bridges that gap between the two antennas then the signal just dies. For me, I bridge that gap each time I use email, send a text message and browse on the web... basically every time I use the phone for anything other than making calls. When making calls it doesn't effect me just because I grip the two edges of the phone and not the area around the black bar.
So how to fix the iPhone 4 reception issues... Steve Jobs basically said in an email to one user that he was holding his iPhone 4 wrong... ie, hold it a different way. Another option is to buy a case for it so that your hand doesn't bridge that gap.
If you hold the iPhone 4 in your right hand, you probably wont see this issue either. Holding the phone landscape to send text messages and browse the web also helps with the issue.
It's a shame really as the phone it's self isn't cheap. The antenna design seems to be amazing in how it works but it seems like they missed one critical point in that you can't hold it if you are right handed in portrait mode unless you buy a case or use it in landscape mode.
Are you having issues with your iPhone 4? Will you be spending £25 on a case? or do you think Apple [AAPL] should be handing them out free to right handed people? It's a shame really as the phone seems so right in every other way and is simple to use... except that you have to write a text and then let go of the bottom of the phone for a few seconds before you send the message.