Is working for a mobile services company in the entertainment sales section (of images and ringtones) unlawful? And is the money earned from it unlawful, given that the nature of the work is purely technical and not related to the content?

There is no harm in non-musical ringtones and selling them, but musical ringtones are not permissible because they aid in sin. As for pictures, it is permissible to sell pictures of non-living beings. Photographic images of living beings are permissible as long as they do not show 'awrah (private parts), whereas hand-drawn images of living beings are not permissible. Jokes that adhere to Islamic guidelines are permissible, but selling them is not permissible if they contain indecencies or lies. If the work is limited to selling what is permissible, there is no harm in it, although it is better to avoid it. However, if it involves selling what is forbidden, it is not permissible to work in it except in cases of extreme necessity. In such a case, the necessity is estimated by its extent, and any surplus beyond the need is spent on the welfare of Muslims. Repairing malfunctions on a website that sells forbidden items (such as impermissible ringtones, pictures, or jokes) is not permissible except out of necessity, because the combination of lawful and unlawful necessitates prioritizing the side of the unlawful.