I'm a web developer, and I'm doing back-end and front-end to a project of the company I'm currently working at. I have a PM (Project Manager) for this project and I do report to him every day.  
  
Recently, the PM estimated hours to conclude a list of tasks (so, a milestone), but he didn't ask me if it's enough (and he passed this estimative to the customer). So, currently, I see this as a miscommunication or missing teamwork.   
  
So I have some specific concerns: 

**1.** Is it correct to the PM define hours without contacting the software's developers?  
**2.** Should I help the PM to estimate hours?  
**3.** Who is the responsible if the devloper can't do the feature in the time allocated by the PM?  

How can I address these concerns to the PM? **Should** I try addressing them?