None of the previous SMS-to-groups threads seemed quite apt (or were very old), so starting a new one

Is there a website that

a) Would allow me to insert staff members' names/cell phone #s, and
b) I could then send a text message to all via a web interface, or
c) Alternatively, send to the group by using a certain email address that automatically triggers a group-send

Initially I would need two groups:

1) One group of about 10 people
2) A second group of about 10 people

(Very occasionaly would need to send to both groups simultaneously)

Later, would like the ability to send to all members (who consent) with a third group which might number up to a 100 names.

Free is better, although cheap and no-ads is ok too

Any ideas?