Glenn Fleshman, commenting on the Flickr set I just deleted because it was a pain to maintain:
The FCC doesn’t require antenna placement. Rather, it requires manufacturers to meet SAR rules: “Any cell phone at or below these SAR levels (that is, any phone legally sold in the U.S.) is a “safe” phone, as measured by these standards.”
Manufacturers typically design phones to keep the sweet spot as far away from the head as possible to make it easier to be below SAR limits while using the maximum possible power under spectrum licensing rules.
Your device may have internal and external antennas. Avoid touching the antenna area unnecessarily while the antenna is transmitting or receiving. Contact with antennas affects the communication quality and may cause a higher power level during operation and may reduce the battery life.
So far, I cannot find warnings of where not to hold a device from Apple, Google, and RIM (besides Apple’s new apple.com/antenna page, of course). If you find any documentation from these companies, please submit using the form on this site and include your name and a personal link in the post. If you have a Tumblr account, your name and blog will be credited.