Where Telephony is a part of android.provider.Telephony which is a part of open source release .
You are not linking to an "open source release". You are linking to an email from 2008.
Here clearly mentioned that "you should not try to use it from your applications."
That phrase is not mentioned in the blog post. That is from an email from 2008.
than how can I find default SMS app in device ?
Use Telephony.Sms.getDefaultSmsPackage()
, as is mentioned in the blog post.