Hi it's me. Hello :)
I have a 3DS Test Unit, which is capable of installing 3DS/DSi applications compiled in the .CIA format from an SD card. So while a way to install applications you create yourself, for normal 3DSs is not possible (i.e. homebrew for 3DS is not yet possible), I am willing to test them for you. I am also in contact with two other people which I may be able to forward .CIAs to for testing if my Test Unit is incompatible with the .CIA. See bottom of page for .CIA testing submission.
 Submitting a .CIA for testing
Make sure you include:
- What the application is supposed to do, and anything you would like me to look out for (outside the actual running of the application)
- What you would like me to record. i.e. screenshots, values returned, etc
- Whether or not I can share the .CIA with other people publicly, privately or at all
- The SDK version and revision the application is built with.
Then once you have all that done send the email to firstname.lastname@example.org
Please note that all .CIAs sent are not installed blindly, each have their title IDs checked to confirm that they will not overwrite/damage any irreplaceable/critical titles.