Facilitate Communications; Don't Proxy Them
In your specific example, the Scrum Master should function as a communications facilitator, not a proxy for the team. The Scrum Master often functions as a switchboard operator by:
- Helping team members to identify points of contact outside the team for collaboration and refinement of Product/Sprint Backlog Items.
- Helping non-team collaborators (e.g. customers or stakeholders) figure out which team members they can to collaborate with to develop or refine a Product Backlog Item.
Clearing impediments should be more about helping the team to help itself than it is about being "the face of the team." If you routinely find yourself communicating on behalf of the team rather than facilitating communications or promoting/clarifying/refereeing the Scrum process, then there may be a process problem with your Scrum implementation.
Caveat: Extending the Role via Working Agreements
As a Scrum Master, you should be encouraging the Product Owner and Development Team to take ownership of the process and craft their own solutions within the tenets of the framework. However, as a member of the Scrum Team, you are an active participant in the process, responsible for fulfilling your core role as well as supporting the the whole team's internal working agreements. Balancing the yin-yang of the coach/referee role with full-fledged team membership within a continuous-improvement process is what differentiates decent Scrum Masters from great ones.
As a full member of the Scrum Team, the Scrum Master can (and often does) take on process responsibilities collectively agreed to by the Scrum Team. This can include delegated authority from the Scrum Team or Development Team to represent their interests with line management and stakeholders, or within certain inter-team processes such as a Scrum-of-Scrums.
The subtle distinction here between speaking for the team as its chosen spokesperson with authority delegated by the team, versus unilaterally speaking as the team based solely on the defined role of Scrum Master, is very important to make. The former is empowering and in accordance with agile principles, while the latter is generally a project smell that indicates an immature agile process. However, it's more of an art than a science; there's a lot of gray area making this a "your mileage may vary" issue that will depend greatly on your project's unique milieu.