REGISTRATION:Register your cellphone to GCASH by sending this text to 2882:
REG<space>4-digit PIN/mother’s maiden name/first name/last name/address Remember! Make sure that your First Name and Last Name match the information that appears in any valid ID of yours. This is important for future GCASH transactions.
HOW TO SEND GCASH:Just type AMOUNT<space>4-digit PIN and send to 2882+10 digit cellphone number of the recipient.
OR
Go to a Globe Business Center
You can go to any Globe Center and request to do a GCASH cash-in transaction. You will need to fill up a GCASH Service Form, and present any valid ID to complete your transaction. Cashing in at a Globe Center is FREE!
Go to an accredited GCASH Partner
GCASH has over 1,800 accredited partners around the Philippines. These include SM Department & Metro Gaisano stores. Just like in a Globe Center, you will need to fill up a GCASH Service Form and present a valid ID to complete your GCASH cash-in transaction. You may be charged a transaction fee, which may vary per partner.
source: http://www.g-cash.com.ph/sectionpage.aspx?secid=25&rand=62 
