But unless you can build a custom casing for it for example, remove the whole board out (carefully and completly discharge yourself before even touching it) and maybe build a casing big enough to support (modified) laptop ram probably and possibly make the device faster and awesome looking as well. Oh, and you may have to modify the chip inside if possible.
Zombie thread comes back from the dead. But I had to respond to address this.
No. Just no. The laptop memory is no doubt going to have different timings from the built in RAM on the SoC. Then you have to power that RAM and whatever controller you install with it. And this completely ignores the fact that you probably still won't get the RAM recognized by the SoC, because nothing on the board or its firmware is looking for any attached out-of-spec, different-timing RAM on a separate controller.
And even ignoring all of THAT... the CPU and GPU probably aren't powerful enough to run iOS4 anyway.
So no, you can't upgrade it. Even if you could, all the effort and cost of materials would likely be more than just ditching the phone and getting the next model up anyway.