Well, one thing for sure, you won't get your replacement on the spot. Waiting time is around 2 weeks, add another week if you're just sending it to a Maxis reseller not the Maxis Centre (some of them ships to Maxis on weekly basis, depending on size).

Your unit will be exchanged with either a refurb or new unit, also partly depends on the cosmetic outlook of your current iPhone. Refurb or brand new, it will come in a sealed plastic pack containing only the phone (no box). So the only way to check either it's brand new or not is by checking its serial/IMEI.