How to text from any PC without knowing the cell phone's carrier?

I would like the best way to text from a desktop or laptop PC without knowing the carrier?
There are a few ways to send a text message from any PC but you have to know the person's smartphone carrier.
Then you create an email to the person's cell phone number followed by "@" and the carrier's domain.
But unlike a cell phone, there is no need to lookup the carrier.
I have about 180 physicians with their independently owned smartphones, and I would like to send a text to all of them or a small fraction of them.   I would like to do this from Windows 7, or 8 or 10.
Thank you.
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David Johnson, CD, MVPOwnerCommented:
Then you would need a SMS provider connected to your phone i.e. google voice, skype (need a subscription), twillio and others
FADugachOwnerAuthor Commented:
Not sure I understand what you mean.  I don't want to send a text to myself?
Again, I want to send a text message from any PC like a Windows 7 OS to any cell smartphone not matter which carrier the recipient is using.
EirmanChief Operations ManagerCommented:
There are some seemingly good free services listed here.
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FADugachOwnerAuthor Commented:
Eirman, this looks good but from your answer it doesn't sound like you have used any of these and can't personally recommend any of the 10 sites.  
Please note that just before the first site it says....
"Even if they aren’t collecting them right now, they could start at any moment, so use these sites at your own risk."
I planned to send information to over a 100 physicians and don't want to start sending them spam.
I'm very nervous about using these services even if they work.
Thank you.
EirmanChief Operations ManagerCommented:
It's now accepted that with most free online services, YOU are the product.
Youtube & Google Maps are perfect examples.
Most mobile providers here in Ireland & UK allow one to send free webtexts.
My provider allows me send 500 free webtexts (including group-texts) per month.
Try your provider.
David Johnson, CD, MVPOwnerCommented:
Then you would need a SMS provider i.e. google voice, skype (need a subscription), twillio and others don't know why I had included phone.

These are services that allow one to send SMS messages. I only included the ones I've used and where myself and the recipient are not the product.  SMS spam can be just as bad as email spam.

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FADugachOwnerAuthor Commented:
That's what I was looking for!
Thank you!!
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