For prepaid users the APN should be "minternet" (without quotes) or "fbband" for postpaid users if you want to use their data service outside of normal BIS coverage. Set it at "blackberry.net" (without quotes again) to prevent the carrier from charging you with extra fees.
Sun also has prepaid BIS in 1/3/7/30-day durations (PHP 50/125/250/1000 respectively), just key in "BB#DAY" (where # is the amount of days ie. BB1DAY) and send to 386. Once you receive the SMS acknowledging your service activation you can then go to Options>Advanced Options>Host Routing Table (OS 5) or to Options>Device>Advanced System Settings>Host Routing Table (OS 6) and use the BB menu to access the "Register Now" option to update your device with SUN BIS. Your device will then attempt to download the appropriate Service Books. Try a device reset/battery pull (by physically taking out the battery or holding alt+right shift+del) if you think your device is not registering properly.
I don't know if Sun has promos similar to Globe's BB Social/Messaging where the service is only PHP 300 per month since I always use the full BIS service.
For power users who want to create/access their push mail account and other BIS settings through regular browsers the Sun BIS site is
http://suncellularph.blackberry.com.
Sun BIS is also good (if not at times better) than Globe BIS. I don't have a third BlackBerry to try out Smart's BIS but I have friends who do and have been happy with their service.
The only advantage (as of July 1, 2011) of Globe over the other carrier's BIS service is that their BBMAX service also covers non-BIS usage for the same monthly fee (999) but the service is sometimes terrible at best.