From Verizon's site:
Just to dispel myths about OTA (*228) programming Options
What does it do? 3 things, and 3 things ONLY.
1) Programs your phone, including your MTN, MIN, and Home SID (represents where you live, and what your home switch is)
2) Downloads Preferred Roaming List, so that your phone will automatically know what network to use when you are not using your home SID.
3) (newer option) you can change your own ESN... just call it from the phone you "want to use" and tell it your phone number... pretty slick!!
Things you should and should not do:
You SHOULD; occasionally update your Preferred Roaming list, From your HOME AREA or another VZW coverage area
You SHOULD NOT; dial *228 in an extended network area. (another carrier's towers) It is totally unnecessary (and honestly a little dangerous) to do this when you reach your destination city.
The endless "beating a dead horse" thread continues here:
Just to dispel myths about OTA (*228) programming - Verizon | Forums and Blogs - Verizon Community