Yes, it has happened and no, I am not lying. A Polish developer named Marcin-PRV achieved this feat by sucessfully installing Microsoft Windows 3.1 on a Symbian S60 powered Nokia N95.
Marcin used Symbian version of DOSBox for installing Windows 3.1, as native installation was not supported. And in the end, the N95 was running both the OSes side by side.
And in case you are wondering whats the whole point in doing something as crazy as this ? i will tell you, its called : FUN. :-). Moreover, these modern day smartphones are more powerful than those PCs which ran Windows 3.1 during the early 90s, so why not utilize your phone's available resource and experiment out something as uber-cool as this.
I just cant wait to get my hands on something like this. Well done Marcin. So whats next in the line-up ?? Microsoft Windows 95 on N96??