Transfer a file from Android to a PC (not in the same network) If I were connected by wifi in my network, there isn't any problem because with AirDroid I can access the sdcard files using the browser.

However when I am out, how can I transfer a file from my phone to my PC? I can access my PC using SSH, but then from the PC I can't access the phone for get file using SCP.

I guess the question is: Is there any app that allow do such action? I think the only possible thing is install a SSH server in the phone, isn't it? Any free (from Google Play) app? I've seen AndFTP but it only allows ftp in its free version.
I think you should try dropbox / google drive.
It will be more flexible than running a separate server on your phone. You will be able to access you file from the cloud at any moment even if you don't have access to your cell or the battery is dead.