Great question — answering as the UphillTech team:
Clickatell is a popular SMS gateway. It works in 200+ countries. Their API offers a choice of connection options via: HTTP/S, SMPP, SMTP, FTP, XML, SOAP. Any of these options can be used from php. The HTTP/S method is as simple as this: http://api.clickatell.com/http/sendmsg?to=NUMBER&msg=Message+Body+Here The SMTP method consists of sending a plain-text e-mail to: sms@messaging.clickatell.com , with the following body: user: xxxxx password: xxxxx api_id: xxxxx to: 448311234567 text: Meet me at home You can also test the gateway (incoming and outgoing) for free from your browser
Full answer by Daniel Vassallo: https://stackoverflow.stackexchange.com/a/1939732 (CC BY-SA 4.0).
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