Hi there! Switching the SIM card to another phone will not switch your account to that phone. You need to swap your phone online. Once it is done the SIM card will no longer be invalid. You can do it here.
That would mean that the phone is not compatible with us. In that case it can not be activated. If Apple confirms that it is a Virgin mobile phone (not unlocked), please call us at 888-322-1122 so we may investigate further.