A method of facilitating access to services of an IP Multimedia Subsystem, by users groups that require alternative handling in relation to the standard handling of IP Multimedia Subsystem users. Functioning instructions are added to the user groups subscription maintained in the IP Multimedia Subsystem, instructing nodes in the IP Multimedia Subsystem to adapt their standard functioning for this specific group of users. The instructions in a subscription of a specific user group, provide a node of the IP Multimedia Subsystem that does no longer need to be specific for certain types of users, but has a standard way of operation, that is modified by instructions for dedicated operation for only that specific user group. In further aspect embodiments are disclosed providing improved solutions for known problems of IP Multimedia Subsystems making use of functioning instructions included in the subscription.