the original poster said they have Cellular One
The way MMS is counted varies by each carrier. Example: Cingular it is just deducted from SMS allotment, but with Verizon it is deducted from the allotment AND counts as one minute of airtime also.
You will have to check with your service provider directly. Unfortunately we can't access their website for you without your zip code since it redirects to other providers that bought out Cellular One in other markets (this market it goes to AT&T)