Click-to-Call in Windows application
Should you need to transform the number before dialing (for example, remove plus or somehow else) please read the article about the dialing rules.
Execute SoftphonePro.exe with -call command line parameter to make a call in your Windows application. You can find detailed description in Command line parameters article.
You can prevent Softphone.Pro Main Window popping on outbound call: How to prevent Main Window popping on incoming or outgoing call?