Holding the phone normally (which is always properly) blocks the antenna, if it must to be at the bottom of the phone it should have been inside the phone like the 3GS.
If you like inferior internal antenna's (that require a higher dBm signal to connect at all, worst case, when used properly), then return your i4 and buy one of those other cell phones.
All products have trade-offs. The i4 is thinner, gets much better reception if used properly, and a worst if not. The 3GS gets measurably worst reception if held properly, but somewhat better in a grip of death. The Droid X is a lot larger than either, but has room for bigger (and more!) antennas. In strong signal areas, they all work. Choose your poison.
Note that the users manual for many other smartphones recommend against holding them around the antenna area for best results. Do they still make cell phones with stick up aerials? Maybe you should get one of those instead of an i4?