I just did a quick Google search and 3 beeps call failed appears to be a common Apple problem
Apparently the top 3 fixes are
1) turn phone off at least once daily to clear memory cache space
2) reduce the number of apps running to free memory
3) put your phone into airplane mode and out right away to try and get a new network connection.
As well you could be in a dead area where your phone is not able to connect.