Praise be to Allah.
Selling and repairing equipment that may be used for good or for evil, for permissible or haraam things, is subject to further discussion:
(a)It is permissible to sell them and repair them for those who it is known or thought most likely will use them for permissible purposes.
(b)It is not permissible to sell them or repair them for those who it is known or thought most likely that they will use them for haraam purposes.
(c)If it is not known, then one should act upon what one thinks is most likely to be the case. If what is usual in your country is that they are used for permissible purposes, then it is permissible, otherwise it is haraam.
What appears to us to be the case is that mobile phones are used for permissible purposes in most cases, unlike televisions. Based on that, there is nothing wrong with you repairing this equipment, selling parts and training others to work in this field, whilst paying attention to two matters:
(i)You should deal with the phone only, and not the chip or memory card. Thus you will be safe from looking at what it contains.
(ii)In the event that you see something that is obviously wrong, whether it is an image or a movie, then you have to remove it, so as to denounce the evil, and you should not pay any attention to the owner’s objections. In this case, you have to advise the owner of the phone and explain to him that this action of his is haraam.
We ask Allaah to guide and help us and you.
And Allaah knows best.