There are several ways to redeem your refill voucher:

1. Redeem your refill voucher online by going to http://www.t-mobile.com/Coupons/default.aspx?referrer=prepaidrefills and entering your T-Mobile USA mobile phone number and the PIN code on your refill voucher
2. Call T-Mobile customer service on +1 877 778 2106 (you can call this number from any phone including from Australia)
3. Call T-Mobile customer service on 611 (from your T-Mobile phone while you are in the USA)
4. Enter *8646 into your mobile while you are in the USA and follow the instructions

Please note that your monthly prepaid plan will start as soon as you have added sufficient credit to your account to cover the cost of your monthly plan. To avoid having your plan start early and expire before your trip has finished it is advisable to wait until the last minute (either the morning of your flight or the day before you travel) before adding redeeming your refill voucher.