The NBTC yesterday summoned AIS staff to its offices |to explain the glitch. AIS explained that the glitch |was the result of a software update on a certain server |to upgrade the service quality. The upgrade impacted about 12,000 customers who use |special value-added services. Of those, 9,208 could not receive calls but could call out, while the rest could receive calls but could not call out. |AIS will send them SMS to inform them about the free call minutes.