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You can also use the 'callto:' format: <a href="callto:{{NUMBER}}">{{DISPLAY VALUE}}</a>.

John,

We are using option #1 having numbers on a web page associated to the TEL Protocol to allow CTD from a web page.  It works most of the time but then there are instances where it won't dial when the number is clicked.  I've looked at task manager when its working and not working and I see a second instance of the softphone.exe kick off but then it stops when it realizes there is already a softphone.exe running.  So it appears that the TEL protocol is kicking off Ring Central's softphone but then the softphone does not make the dial.  If I completely stop the softphone (no instances running) then start it back then clicking a number will once again initiate the call from the Ring Central Softphone.  

You can set up click-to-dial from RingCentral in 3 ways:

1. URI Scheme: If a phone number hyperlink can be made using the "rcmobile" or "tel" URI scheme, that can be used to make a call from a RingCentral softphone installed on the same computer. Some solutions support the "tel" URI scheme out of the box so this may work already if you can use the RingCentral softphone.
2. RingOut: Our RingOut API is a REST API that can dial from any phone by connecting two phone numbers. This approach gives you flexibility in choosing your dialing phone, e.g. a desktop softphone, physical phone, mobile phone, etc.
3. WebRTC: We recently released our WebRTC capability and SDK as beta. This will allow you to make calls from inside a WebRTC enabled browser. The SDK an demo app are available here:

https://github.com/ringcentral/ringcentral-web-phone

Given the above, let us know what you have tried so we can assist.