With Sun cellular's Text All 15, you can send 100 free text messages to other networks and 50 free text messages to your fellow sun subscribers ,1 whole day, for only P15.
You may want to check this post, this is the new TextAll offering from Sun Cellular http://mobile.gjamoroso.com/2013/01/sun-text-all-199-power-up-adds-up-1000.html
To register just text the following to 247
Enjoy it prepaid sun subscribers while it last (until October 5, 2010 only).
Thanks symbianize for the tip.
Update: Sun change this promo to a newer allocation of free text, click this link to view more info
And if this is not enough for you, try out the new Sun Super Loaded 25 with free mobile internet.