I need to know how to get the best credit card rate.  Currently I am
getting my customers credit card numbers in the field and bringing
them back to the office and keying them in.  I pay 2.4% plus $.25 on
each transaction.  What is the best solution?  A mobile device I bring
in the field so I can swipe the card - resulting in a lower rate?  Who
are the players, what are the different plans, rates, devices, etc.  I
need a complete analysis.

I understand you are looking for the charges and rates charged by the
credit card provider to the merchant for the service and not the rate
provided by the credit card provider to the consumer. I found that
when I directly asked several banks and credit card providers for
rates for this type of service that the rate varied depending on the
anticipated volume of usage and the type of industry/merchant. Higher
volume favoured lower rate. Lower risk to the bank favoured lower
rate. In the case of banks my existing position as a customer gave a
more favourable rate.

I had a mobile card swiper for housecalls but stopped because the base
rate included a $16 per month fee for the cell phone in the unit. Now
I key in the number when I return and added two bucks to the house
call fee.

With any 'Mobile' or 'Wireless' product there will be costs associated
with the portability of the unit.  However - the differentiation in
the rate for a 'swiped' or 'mag-stripe-read' transaction can far
outweigh the additional costs associated with the mobile units. 
Bottom-line is HOW MUCH ARE YOU PROCESSING?  Typical difference
(ball-park) between a swiped transaction and one that is keyed is
roughly .45 - 1.25% (actual rates differ based on average ticket size,
and pricing structure - but its a good acid test).

If you are processing over $2m (2,000) per month - you will likely
benefit from the mobile technology.