Did you know that you can have old Windows versions on your Symbian S60 smartphone? It's using the DosBOX emulator ported to Symbian in order to do that, so it's just like an application, no need to replace the operating system (I don't even think that's possible).
Here's a blog I made containing almost exactly the same tutorial: http://win4symbian.blogspot.com/
This particular tutorial is for Nokia phones, but it might work with others that have Symbian OS.
What do you need?
A Symbian s60 v3 or v5 Smartphone with at least 16MB memory card
One USB cable or card reader
Internet Connetion (lol?)
Step 1: 1: Download.
It has everything you need to install. I made it zip, so you can download it directly from the phone. Unpack it somewhere.
Warning! Although Windows 3.1 is very old and it might be abandonware, please use this ONLY if you also own a copy of MS Windows 3.1.
Step 2: 2: Installing DosBOX
Set your date to Jully 2008 before installing 4 - SDL-1.2.13-s60-2.3.4_armv5, or you will get an expired certificate error.
Also, set your date to August 2009 before installing 8 - dosbox.
Step 3: Installing Windows 3.1
Unplug the USB and plug it back. Set your phone to Mass Storage.
Copy all of the contents of the folder "memory card" to your phone's memory card.
* If your phone has a normal screen (eg. Nokia N95), copy Data\WIN3\Orientation\normal\dosbox.conf to e:\Data\ on your phone, where e:\ is your memory card.
* If your phone has a landscape screen (eg. Nokia e63) you don't need to do anything, because it's already set to that. Anyways, if you screw up and your screen is rotated 90 degrees, copy Data\WIN3\Orientation\landscape\dosbox.conf to e:\Data\ on your phone, where e:\ is your memory card.
* In order to change the resolution from 640x480 to 320x240 in Windows 3.1, you need to change the drivers. I made this simple: copy Data\WIN3\SMALLRES\system.ini to e:\Dos\C\WINDOWS\ in order to set the resolution to 320x240. If you want to revert back to 640x480, just copy system.ini from Data\WIN3\normalres in the same folder. It's already set to 640x480 so you don't need to do any changes. Also, Calmira screws up in 320x240, so I don't recommend it.
Step 4: That's it!
Enjoy your Windows 3.1 ! :D
It's a bit slow, but it works.
Here's a video: