strncpy and using sizeof to copy maximum characters

strncpy will not null-terminate the destination if it truncates the string. If you must use strncpy, you need to ensure that the result is terminated, something like:

strncpy(call, info.called, sizeof(call) - 1);
call[sizeof(call) - 1] = '\0';

BSD's strlcpy(), among others, is generally considered superior:

http://www.openbsd.org/cgi-bin/man.cgi?query=strlcpy

If the source's length is less than the max number passed as third parameter strncpy will null-terminate the destination, otherwise - not.

If the source is equal or greater in length than the destination - it's your problem to deal with it. Doing like you suggest - calling strlen() - will not work since the buffer will be not null-terminated and you'll run into undefined behaviour.

You could allocate a bigger buffer:

char buffer[bufferSize + 1];
strncpy( buffer, source, bufferSize );
*(buffer + bufferSize ) = 0;

Your idea:

call[strlen(call) - 1] = '\0';

would not work, as you would be calling strlen() on a non-terminated string