As you might be well aware, default is a condition which is pre-determined or pre-set by the programmer/manufacturer and which we happen to see whenever we operate the machine (here it refers to mobile phone).

I personally feel that transliteration holds the key while translating such type of texts and one should not hesitate to transliterate such terms PROVIDED these are competent enough to communicate the desired meaning.

I have proposed three options and hope that one of them could serve your purpose.