Check out this guide on how to have unlimited access when using Yahoo Messenger on your mobile phone / cellphone.

Get Yahoo Mobile Messenger unlimited access
(Open to Globe Postpaid and Prepaid subscribers only)
- Get the myGlobe Connect settings on your phone for free, text GO <phone model> to 2951 and save settings.
- Type www.unlichat.com in your phone's internet browser.
- Click 'download' and install UNLICHAT when prompted.
- Launch UNLICHAT from your Applications folder. Make sure you use myGlobe Connect APN.
- Enter your Yahoo ID and password. Start chatting.
P25 - Unlimited access for 1 day.
P100 - Unlimited access for 5 days.
P200 - Unlimited access for 15 days.
Click here for more information.