You have to enable the roaming mode before leaving the Philippines. If bought there, roaming mode is not enabled by default. If already abroad you can't do it as of course you do have the network.
How to activate Globe Roaming
Here’s how you activate Globe Handyphone Prepaid International Roaming.
Just text GROAM ON [Start Date] [No. of Days] and send to 2884.
For example, if you want to activate your roaming on September 26, 2005 for ten days, just text GROAM ON 09/26/2005 10 send to 2884.
Make sure that you have P100 balance before activating your International Roaming. You also need to maintain P100 daily load while abroad to ensure continuity of your roaming service. You may request for roaming activation 7 days before departure or at least an hour before departure. Maximum number of days for activation is 180 days.