sc.SendSms("+12345", "Test", "+12345");

Dont work, just work if i put null at last argument:

sc.SendSms("+12345", "Test", null);

Please....Take the time to review the documentation when you think you have a problem:

"HRESULT SendSms([in] BSTR TargetNumbers,[in] BSTR MessageText,[in, defaultvalue("")] BSTR ReplyToNumber,[out, retval] ISmsMessage **pMessage)
This command sends an SMS message.

Parameters:

[out] TargetNumbers contains a comma-separated list of target numbers.

[out] MessageText contains text of the message to send.

[out] ReplyTo contains the reply-to number.

[out] pMessage receives the interface pointer for the SmsMessage object."

From: https://developer.skype.com/Docs/Skype4COMLib/ISkype#SendSms

Also See Example:

https://developer.skype.com/Docs/Skype4COML...cemailServer_cs