Hi, I just discovered this a month ago and tried it out and it works just fine.
For this tutorial, you'll need:
1) A jailbroken idevice (Cydia).
2) A computer.
3) WinSCP.
4) Wifi.

GpSPhone is a Gameboy Advance emulator, just like desmume on the computer.
What it does is "emulate" the Gameboy.
Note that this doesn't just work for Pokemon, it works for any Gba game.
Yugioh GX Duel Academy, Kingdom Hearts etc. etc.
WinSCP enables your iPod to connect to your laptop through Wi-Fi (no cable needed)
PS: gpSPhone costs money.
However you may get it free through xsellize etc.
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Okay, first of all, we'll start by adding Cydia.xsellize.com as a repo.
Then we'll search GpSPhone+ Bios.
If for some peculiar reason there is no Bios included, download it separately.
Then we have to download OpenSSH, too. (Cydia)
It enables WinSCP to function with your iDevice.
The next step is downloading WinSCP and setting it up.
Download it here:http://winscp.net/eng/download.php
Make sure you have the same Wi-Fi for your PC as the idevice's Wi-fi.
After you set it up, open WinSCP.
Open WinSCP. Click on "New", which is above "Edit".
The host name is your IP Adress, which you can easily get through going to Settings, Wi-Fi, then clicking on the Wi-Fi your idevice is using and you'll find it above the Subnet Mask.
Write the IP Adress as the host name.
Username= root.
Password= alpine.
It will give you a warning message the first time you connect, just click on "Yes" on the left.
I advise you to disable Autolock, because it might cause errors during the connection.
If you've done everything correctly, you'll see your Computer's files on the left and your iPod's on the right side.
As it might be illegal, I will not link you to Roms.
Only download Roms from the internet, which you have in real life.
Download Roms from a trusted site on your computer and add the .GBA file on your desktop, to make things easier.
Now go back to WinSCP and go to /private/var/mobile/Media/ROMs/GBA.
This is basically gpSPhone's in this case empty ROM folder, an easy method is to copy the Rom from your desktop (left click, copy.) then clicking ctl+v, which is basically paste, when you're in the ROMs folder in WinSCP.
It will ask you to copy [romfilename].GBA to remote directory /private/var/mobile/Media/ROMs/GBA, say copy.
This might take a few minutes, so in the mean time grab some popcorn or something.
After it copies, you'll see the Rom in the folder.
Now open GpSPhone and voila.
Note that the Roms will also work on a Computer Gameboy Advance Emulator.
Thanks.  

Seems legit.  

I was looking for how to do this. I used to know how, but since I haven't done it in forever, I forgot. Thanks!  

Why do all copy me lately?  

So it is legit :O I knew it!!  

It should be noted that GPSPhone usually costs money, unless you get it from one of the sources that lets you download it cracked. Which is where you probably should get it from anyway.  

Posted by Psycher!

It should be noted that GPSPhone usually costs money, unless you get it from one of the sources that lets you download it cracked. Which is where you probably should get it from anyway.

Thank you, I didn't know that.
(Too many sources with cracked packages installed )  

For those who don't have a source that lets you download cracked Cydia programs such as GPSPhone, you can use cydia.xsellize.com. It's a generally reliable source with a large selection of stuff.  

Posted by Alexei

If you won't reply to me.Then ok.

**** off attention-*****.  

Thanks Dimentio, I appreciate the tutorial worked for me.  

You're welcome.  

This is useful because the programs on Cydia for downloading ROMs don't work for crap.  

Posted by Psycher!

This is useful because the programs on Cydia for downloading ROMs don't work for crap.

Exactly. Unlimrom is bullcrap.  

Posted by Dimentio

Exactly. Unlimrom is bullcrap.

I had EmuRoms and it crashed the second I tapped a genre of games. EVERY TIME.  

By the way, have you tried my method yet?