I use only Linux in my machines. I think that Ubuntu Linux 12.04 is usable enough to everyday but sometimes we need to use some restricted softwares and i have a virtual machine to run Windows XP, Windows 7 to get access to these programs.

Games are a trouble for virtualization but it is not a problem for me.

In the case of Nokia N900, we have the Nitdroid that is not totally completed, it`s useful, but is not completed. I think that the user experience can be better when we have a "VirtualBox for ARM" that we will run "iOS, Symbian, Android 4" in a virtual machine.

We don`t need a new operating system for N900 to do the same thing that we can do with Maemo. We need to have access only to a greater amount of softwares and integration between these operating systems.

I don`t know if it exists, the most seamless solution seems to be the QEMU but it is to run ARM systems in X86 computers or X86 in PowerPC computers.

This solution for me, is the solution for all problems about softwares in cellphone.

Why someone has not thought in this solution yet?

Here you go: http://lmgtfy.com/?q=arm+virtualization

There are primarily two things that are required for running usable, responsive virtual machines: CPU power and RAM
Unfortunately, the N900 is sorely lacking in both.
Yes, the CPU can be overclocked (in some), but that only goes so far.
The RAM cannot be upgraded so you are stuck at 256MB, no matter what you do.
Virtual memory is of little use here, since it is thousands of times slower than RAM... the N900 already suffers greatly when using only a couple hundred megabytes of swap (which it does only running 1 OS).

The N9 would be a much better target due to it having 4x the RAM of the N900.

We'll have to wait for Cortex-A15 processors with ARM Virtualization Extensions before even trying to have everyday-usable virtualization on phones.

Currently, the only virtualizers on ARM I can see being used are emulators, which are incredibly slow in their current state.

For now, we can work with chroots, while they don't separate host and guest memory areas and processes, they do offer native code execution and much lower overhead than emulators.

Why viritualize the cpu? wouldnt it be better to somehow run those oses without cpuemulation?

Yes, and this would be greatly accelerated by the ARM virtualization extensions (giving the guest OS almost direct access to the CPU, instead of passing all instructions to a host process which passes instructions to the CPU and back)

Why we need to have native solution? When we will have Windows Phone 7 natively running in N900? Never... but running in virtual machine, we can think that will be easy to get advantages that each system have. All existing softwares in the world can be used in my cellphone, without issues.

VMWare had shown something - Horizon Mobile I think - that was a stab at virtualizing mobile OS on other OS's. Same for Alien Dalvik which basically added a layer to allow for Android app usage on other mobile OS's.

Blackberry has the Runtime for Android apps, so it's not that folks haven't thought of this - I swear VMWare showed virtualization on an iPaq 2210 back in 2003 - but nobody has done this to a point where we'd call it a success or that it's been highly visible.

Alien Dalvik got close, but they switched to a model whereas they wanted an OEM to buy it. Nobody bought it.

So not only have you figured out a way to upgrade the RAM, but you've also found a way for the ARM architecture to run x86 software without emulation? You should patent that as the chipmakers themselves can't do that.

Seriously - the N900 flat out doesn't have enough RAM, there is no way to change that.

Just look at how much swap space the default OS uses... then look at NitDroid and all of the other OSes that run on the N900. Every one of them is RAM-starved. Running more than one at the same time will only compound that problem.

If you followed the link I posted above, you'd see that VMWare demoed virtualization on ARM back in 2009... but it's not available yet. If they can't get it working in a marketable state on current hardware...
You also would have found (as others have pointed out) that a new ARM CPU coming out soon will have virtualization extensions that will make this much more feasible.
But... there is no way to upgrade the CPU in the N900 - so even that is pointless to think about when you're talking about this particular device.

Just to make it clear for the others out there, Alien Dalvik and BB Runtime for Android are not virtualizers. Instead, they're API shims, similar to Wine.
OTOH, Horizon Mobile would be like using your phone like this:

Would windows phone 7 really be interesting to run!? dont think so...
Android is enough for appz since most locked down appz is made for both android and ios sumultaneously, and android is open enough to make an api interface for.
unless the only thing in android thats actually needs to be emulated is the android-java implementation ofcourse...