They say only 50% of your marketing actually gets you a return on investment.. But you can't know which 50%. Not any more. Track all of your calls from cradel to grave, and see where you are getting the most for your money.
Units are a simplified way to calculate overages.
The base of a unit was one local call minute.
Things that count as 1 Unit:
Things that count as 2.5 Units:
SMS - Simple, short text messages
MMS - Longer, or Multimedia text messages