Spok Holdings, Inc., through its wholly owned subsidiary Spok, Inc., is engaged in healthcare communications. The Company offers a suite of unified clinical communication and collaboration solutions that include call center applications, clinical alerting and notifications, one-way and advanced two-way wireless messaging services, mobile communications, and public safety solutions. It offers its services and products to three market segments: healthcare, government, and large enterprise. Its one-way messaging consists of numeric and alphanumeric messaging services. Its two-way messaging services enable subscribers to send and receive messages to and from other wireless messaging devices, including pagers, personal digital assistants, and personal computers. The Company also offers voice mail, personalized greetings, message storage and retrieval, and equipment loss and/or maintenance protection to both one-way and two-way messaging subscribers.