If I were his (the person with new mobile phone) friend, I'll remind him to use his time wisely, and consider his priorities. Playing games (short-term happiness) is not bad, but if it's negatively affecting what is most important in his life, that is, his education as preparation for his future (long-term), then it's not good for him.
Addiction is not only in substance, but also in form. Spending too much time playing games is addiction in form, so you should tell your friend to change his ways before it's too late, and his grades badly affected.
Help him to list down his goals (start with short-term as in getting better grades in school), and how to reach/accomplish these goals.
