Hi Shane1992,
One possible reason why the police seized your mobile is because it forms evidence, or contains evidence, that can be used against you. The police have agreed to recommending you for the diversion program. The diversion program means that the police agrees to withdraw their charges against you, in exchange for you completing some kind of program (your conditions). This is an arrangement between you and the police (with the court registrar's consent). Because the police withdraws their charges, you will not be found guilty and convicted (and it will not appear in your criminal record). However, if you fail to meet the diversion requirements, the police can resume their charges against you, which will require evidence (i.e. your mobile phone).
Hence, they might hold onto it until you complete the diversion program. Then, they should return it to you within a reasonable time (e.g. one week). They should not be holding onto it permanently because they will not charge you and you will not be convicted. If they refuse to return it after a reasonable time, you can apply to the Magistrates Court for the return of your property.
