I later learned of an address which coincides with the signature your
service provider supports. Easy eh? Now I'm wondering if there is some way
for a person receiving an SMS text message to reply or forward the text
message. It doesn't seem like it at the moment.

We're thinking SMS is a way to simultaneously send out a short text message
to a couple dozen people who carry phones around but we must make it really
easy and as fast as possible for those who receive the text message to reply
so we can assign the first one to reply a job. Think of a group of
contractors signed up for a job and when the job is available they all get
an SMS text message and the first to reply gets the job.

We were thinking of using SMS because all current phones appear to support
SMS but all of the different browsers and complexity of developing mobile
applications for all of the different phones and carriers make it a big
expensive pain in the a.s to make this line of business work out. In other
words, we cannot compel everybody to use Windows Mobile phones.

If you are talking about sending SMS from computer to cell phone:
My communication company has special email addresses in form of
<cell phone number>@sms.mts.com.ua.  You can send there an email and
the text in email will
be delivered to corresponding cell phone. So sending an SMS to a cell
phone number in this
case is just sending email to this address. And there are a lot of
APIs to send emails.
I suppose most communication companies have the same kind of service.

If you are talking about sending SMS from mobile device, I think you
can start from here:
http://msdn2.microsoft.com/en-us/library/aa446545.aspx

Thanks,
Sergey Zyuzin.