So you need to learn about SIP....

Well you can get trained by an Instructor, learn at your own pace with eLearning of try a mix of both. All up to you but to survive in the world of SIP and VoIP, getting expert help is always wise - Good Luck on your journey...

And for recognized certification, why not check out the SSCA™ ... Not matter where you get trained on SIP you can take this certification and get recognised as a SIP expert...