A system and method are provided for reliable activation and attachment of mobile devices. An activation server receives, from a client device, a subscription request for accessing a network, wherein the subscription request includes a first identifier of the client device. The activation server determines, based on the first identifier, whether a pending subscription account exists or a new subscription account is to be created. Upon determining that the pending subscription account exists or the new subscription account is to be created, the activation server releases the pending subscription account or creates the new subscription account, and instructs the client device to remove a second identifier from the client device and to use the first identifier for attaching to the network.