Missouri regulators will investigate whether a growing number of consumer complaints about the state's local telephone services indicates system-wide deterioration, the Public Service Commission announced Thursday.

Consumer complaints and inquiries to the PSC regarding telecommunications service quality dropped since 2006, until recently. The commission recorded 332 complaints in the fiscal year ending June 30, compared to 255 complaints during the previous period.

In a motion to open a case, the commission's staff raised questions about whether the state's wireline infrastructure is properly tested, maintained and replaced when broken.

If the commission's investigation ends up blaming phone companies, it can seek to withdraw waivers that frees most telecommunications providers from PSC oversight when it comes to service-quality issues, said Natelle Dietrich, the commission's director of utility operations. She said a company would first be given the chance to fix the problems, then a hearing would be held on whether the waiver would be pulled.

Members of the public can chime in on the quality of their local phone service on the commission's web site, psc.mo.gov, or by mailing comments to P.O. Box 360, Jefferson City, Missouri 65102. The reference number for the case is TO-2011-0047.