We describe and evaluate a new telemetry system based on GSM (Global System for Mobile Communications) mobile phone technology that may provide mark-recapture data for single year survivorship studies. These phone-tags automatically attempt to send an SMS text message once every two days. The successful receipt of a text message ashore constitutes a resighting event within the coastal zone of GSM coverage. Haul-out data and coastal location data are incorporated into the messages. Data are presented for a three-month period (January-March) following tag deployment on 59 gray seal (Halichoerus grypus) pups at the Isle of May (Scotland). An average of 15.5, 4.1, and 8.2 seals succeeded in registering within each three-day period in January, February, and March, respectively. Tags registered with a wide geographical range of GSM radio cells on the Scottish and English east coasts, and also from Norway and Germany. Haulout records covering 54% of the animals' time were received. With future modifications to the tags, this figure should approach 100%. The median delay to network registration was 9.6 sec from a seal in the sea (not hauled out). These data show that GSM mobile phone telemetry is a useful technique to obtain haul-out and mark-recapture data.