You are using an array not a string. So you need to access all elements of array to add as suffix.
Use this :
for(int i = 0 ; i <[phoneNumbers count]; i++)
{
NSString *str = [@"tel:" stringByAppendingFormat:@"%@",[phoneNumbers objectAtIndex:i]];
str = [str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSURL *phoneUrl = [NSURL URLWithString:str];
NSLog(@"Some Text %@", phoneUrl);
}
EDIT : Url was null because there were spaces in "2013-05-31 14:58:24.759 GTCallBack[8225:c07]" so encode it to remove spaces. Hope it helps you.