Abstract: A feature checker provides the ability to review communications service features for interaction problems at service creation time, or at runtime. Hence a feature can be reviewed against existing service features or against a specific other user's features. The feature checker is based on modelling communications service features as constraint satisfaction problems in which constraints 600, 605 determine preset relationships between values 610, 615 for variables 200, 215, 300, 400 of the feature. The model can then be searched for inconsistencies which indicate feature interaction. Interaction can be solved by building in an “alternative invoke” 610 for a feature which overcomes the inconsistency. This might be for instance a form of invoke which, when instantiated, actively suppresses a conflicting feature.