There are two ways reservists can be recalled to active duty -- either voluntarily or involuntarily.
Voluntary Activation - Airmen’s availability to support a contingency is considered as part of the selection criteria. Their commander or commander’s representative may call and ask if they are available and willing to be activated.
Involuntary Activation - Airmen of the Selected Reserve (IMAs and Unit Reservists) must be available to report within 24 hours of notification. Members assigned to the Pre-trained Individual Manpower, which include the Individual Ready Reserve, Standby Reserve and Retired Reserve, will report NLT 30 days after receipt of orders.
For this reason, it is extremely important to maintain accurate mailing and email addresses, as well as phone numbers with ARPC and, for participating reservists, with your military supervisors and units of assignment/attachment.