Seeking info on how various cell carriers/devices handle email toSMS?

My company uses email to SMS(example: we send an email to
9999999999@vtext.com or 9999999999@messaging.sprintpcs.com) to notify
clients of urgent events. We are trying to generically format the SMS
in a way that will display properly on any cell network or device(cell
phone, PDA, etc...). My main issue is making the most of the160
characters. I am looking for info how various networks/devices affect
the following:
How my character allotment is utilized?
Do the From: and Subject: fields affect my character allotment?
Truncation if character allotment is exceeded?
Multiple messages if character allotment is exceeded?