my samsung mobile GT-C5180 but when i make call then call has disconnected and when i switch off and on then may be work but after some time like 20 minute it's show same problem again and even i cannot received call. but this phone i am buy from hongkong and using now in hongkong with hongkong 3g sim card and if i used this phone in india with indian sim card then no any problem but if i used my hongkong 3g sim card with other handset then also no problem so please let me know if you have any solution of this problem ......Thanks in advance