Are Iphones' content encrypted? Recently I heard that the content of an Iphone is stored in encrypted form meaning that if I were to take apart the Iphone and managed to extract the memory and read it, I wouldn't be able to get any information out of it.

I find this hard to believe because an Iphone can be unlocked and opened in a mater of seconds, the decryption of 16 gigabytes of data in that short a time seems too fast to me. I would like to know what is happening exactly.

Is the memory not actually encrypted, is decryption actually just that fast or is there something else happening.

Just to be clear, my impression was that when you unlock the phone (not just when you turn it on initially) everything is decrypted. obviously turning on the phone provides more than just a few seconds of time to decrypt the phones content.

Additionally, I would be interested not only in Iphone encryption but also the encryption of Androids and other smart phones.
The iPhone is built with encryption inserted automatically when writing to flash memory and decryption inserted automatically when reading from it. This happens with all files, all the time. There is no concept of "decrypting a file and then opening the decrypted file", as there would be on a PC.

No file can be decrypted without the proper key. Some files (such as the ones needed to start up the phone) are decrypted with a key that is always known to the encryption/decryption machinery. Other files are decrypted with a key that is only provided to the machinery once the phone has been unlocked.

That is why unlocking the phone is fast. All that happens is that an additional key is made available to the decryption machinery, so that it is able to decrypt files encrypted with that key.

All this is an over-simplification, since there are more levels of keys than this. The absolutely authoritative source, which is also remarkably easy to read, is Apple's own iOS Security Guide.