This is what I've got when I tried to echo json_encode($data)
{"customer":{"accepts_marketing":false,"created_at":"2014-01-14T12:22:35+08:00","email":"testmail@gmail.com","first_name":"test","id":"185488725","last_name":"testagain","last_order_id":null,"multipass_identifier":null,"note":null,"orders_count":0,"state":"enabled","total_spent":"0.00","updated_at":"2014-01-14T12:30:29+08:00","verified_email":true,"tags":"newsletter, prospect","last_order_name":null,"default_address":{"address1":"sanluis","address2":"san jose","city":"anipolo","company":"","country":"Australia","first_name":"test","id":"185488725","last_name":"testagain","phone":"2312313","province":null,"zip":"1980","name":"test testagain","province_code":null,"country_code":"AU","country_name":"Australia","default":true},"addresses":[{"address1":"sanluis","address2":"san jose","city":"anipolo","company":"","country":"Australia","first_name":"test","id":"185488725","last_name":"testagain","phone":"2312313","province":null,"zip":"1980","name":"test testagain","province_code":null,"country_code":"AU","country_name":"Australia","default":true}],"metafields":[{"key":"contact_number","value":"0654015","value_type":"string","namespace":"global"},{"key":"date_of_birth","value":"01-14-2014","value_type":"string","namespace":"global"}]}}