A few weeks ago, we purchased two Sanyo cellphones (4900 & 8100) and have noticed that during use, especially longer periods of use (20+ min. calls) they get "warm." The warmth is located mostly in the battery but is also noticeable in the screen area. Our previous cellphones (Nokia)didn't do this but they used a different type of battery ... is there anything wrong with our phones or is this "natural" with the newer LiIon type batteries?
the warmth is from the heat generated between the phone and the battery... i think since NOKIA uses an internal battery the heat is not as easily felt thru the plastic shell of the phone. it is natural and every cell phone i've ever used - around 20 or so - have done it! SANYO does seem to get the hottest, the phone that I had that go the hottest was the SANYO SCP-6200(dual band slim phone) it was too hot to hold against my ear before, but my calls can last 2+ hours too.
Should be normal and expected, especially if you're going from a non-colored screen to a colored screen. Also, try turning the display light and keypad light to the lowest settings. If the have these set on "flip open" or "always on", this will cause the phone to get hot when your on the phone for extended periods of time. This will also suck the juice from the battery as well.