A method for management of dynamic Push To Talk, PTT, geotalk groups among members of two or more agencies associated with an incident, wherein the two or more agencies communicate (105, 120) securely, wherein an agency includes a collection of communication resources having an administrator, comprising: creating an incident control area associated with a geographic demarcation of an incident area; electronically transmitting information about the incident control area to the two or more agencies; establishing a talk group permission rule associated with the incident control area for creating an invitation to join a PTT geotalk group; electronically transmitting a joint invitation to the two or more agencies for access to PTT mobile unit users that meet a criteria, wherein the joint invitation includes a request for location information; electronically receiving an acceptance to the joint invitation that includes a User Identity and Credentials of a first PTT mobile unit user, wherein a dynamic access permission managed by a first agency determines what information associated with the User Identity and Credentials of the first PTT mobile unit user are available, and wherein the dynamic access permission changes in real time; based on the dynamic access permission, obtaining a location of the first PTT mobile unit user in real time; when the first PTT mobile unit user is in proximity to the incident control area or is present in the incident control area, determining whether the first PTT mobile unit user is authorized to enter the incident control area based on the dynamic access permission; and when the first PTT mobile unit user is authorized to enter the incident control area and the talk group permission rule is satisfied, electronically transmitting the invitation to join the PTT geotalk group to the first PTT mobile unit user. creating an incident control area associated with a geographic demarcation of an incident area; electronically transmitting information about the incident control area to the two or more agencies; establishing a talk group permission rule associated with the incident control area for creating an invitation to join a PTT geotalk group; electronically transmitting a joint invitation to the two or more agencies for access to PTT mobile unit users that meet a criteria, wherein the joint invitation includes a request for location information; electronically receiving an acceptance to the joint invitation that includes a User Identity and Credentials of a first PTT mobile unit user, wherein a dynamic access permission managed by a first agency determines what information associated with the User Identity and Credentials of the first PTT mobile unit user are available, and wherein the dynamic access permission changes in real time; based on the dynamic access permission, obtaining a location of the first PTT mobile unit user in real time; when the first PTT mobile unit user is in proximity to the incident control area or is present in the incident control area, determining whether the first PTT mobile unit user is authorized to enter the incident control area based on the dynamic access permission; and when the first PTT mobile unit user is authorized to enter the incident control area and the talk group permission rule is satisfied, electronically transmitting the invitation to join the PTT geotalk group to the first PTT mobile unit user.