Improve Interoperable Communications for First Responders Act of 2005

Improve Interoperable Communications for First Responders Act of 2005 - Establishes an Office for Interoperability and Compatibility (OIC), headed by a Director, within the Directorate of Science and Technology of the Department of Homeland Security (DHS).

Requires the OIC Director to: (1) assist the Secretary in developing and implementing the program to enhance public safety interoperable communications at all levels of government; (2) carry out DHS responsibilities and authorities relating to the SAFECOM Program; and (3) conduct extensive, nationwide outreach and foster the development of interoperable communications systems by state, local, and tribal governments and public safety agencies, and by regional consortia thereof.

Amends the Homeland Security Act of 2002 to direct the Secretary to conduct a nationwide assessment to determine the degree to which communications interoperability has been achieved to date, and to ascertain the needs that remain for interoperability to be achieved.

Requires the Secretary to: (1) establish a comprehensive research and development program to promote communications interoperability among first responders; and (2) make grants to states and eligible regions for initiatives necessary to achieve short-tern or long-term solutions to statewide, regional, national, and where appropriate, international interoperability.