Alan,

Ok, let's get the KISS Principle out here...  To get the dumbest thing out of the way, are all these numbers cell phones capable of receiving text messages? 

Second, all you need to do with the iPhone is put the number in your TO field of a text message.  Alternatively, if it is easier, you can activate the Dictate button on the keyboard and speak the number or use SIRI to do it.  If the person is in your contacts, you could say "Send a Text Message to Alan Downing", if you want to send it to more than one person, you would say "Send a text message to Alan Downing and Tom Behler and Steve Pollo", assuming you have all of us in your contacts.  Then, Siri will ask what you want to say and you could dictate that or type it.  If you start a message using SIRI, then you  have to find the edit message.

As to the person that wanted to text using their computer, you have to know the cell provider for each person.  For example, [log in to unmask] or [log in to unmask]

Steve, K8SP for Verizon, .