Let's change that annoying Yoigo logo. The responsible file in this phone is /cust/yoigo/es/logo/oemlogo.mbn, it took me a white to figure out how to deal with this in Linux, so I'll write it here so that I can refer back here when needed.
First, choose an image, edit it, do whatever, and make sure its size is 320x480px and it's in png format. The one displayed in this article is perfect for the task, besides being also yummy ;)_ Then, run this on your new image file:
$ ffmpeg -vcodec png -i imagen.png -vcodec rawvideo -f rawvideo -pix_fmt rgb565 oemlogo.mbn
You then need to put that file into your phone, concretely, as /cust/yoigo/es/logo/oemlogo.mbn. I suggest backing up the original file, just in case. After that, you will need to run this, also in the phone: