Many ways as long as you have a smartphone
1. Subscribe to Globe supersurf 999/unlisurf 999
2. Once you have data or even wifi, download viber, skype, facebook messenger, tango, chaton, for iPhone is imessage. Those can send unli sms to anyone around the globe as long as same platform., i.e. viber to viber. If this cost much try to do the math, 999/15 = approx 66 sms only.
BTW why 15/sms? Are you using globe roaming?
You can avail ITXTALL30 and send it to 8888 at Php 0.30 per text whether local or international.
for more details you can check it here. ->> http://www.globe.com.ph/itxtall30
then click on FAQs.
This is for Globe Prepaid subscribers only.
If you are both using an Iphone,
How bout Imessage thru wifi? or Facetime?