Need logic to collate data
I inadvisable to use Datetime type for your answer_time, change it to TIME type because the 000-00-00 will fail with all datetime functiosn (look at the MySQL documentation : link).

So, when your table looks like : 

[09:47:55] [DEV\MFO] mysql&gt; desc MFO.phone_call;
+-------------+------------+------+-----+---------+-------+
| Field       | Type       | Null | Key | Default | Extra |
+-------------+------------+------+-----+---------+-------+
| phone       | bigint(20) | YES  |     | NULL    |       |
| answer_time | datetime   | YES  |     | NULL    |       |
+-------------+------------+------+-----+---------+-------+
2 rows in set (0.00 sec)


You could try that : 

SELECT phone, 
   Count(*), 
   Count(CASE 
           WHEN Time(answer_time) = 0 THEN 1 
         end) AS NOT_ANSWERED, 
   Count(CASE 
           WHEN Time(answer_time) &gt; 0 THEN 1 
         end) AS ANSWERED 
FROM   MFO.phone_call 
GROUP  BY phone; 

+-------+----------+--------------+----------+
| phone | count(*) | NOT_ANSWERED | ANSWERED |
+-------+----------+--------------+----------+
| 11111 |       21 |           10 |       11 |
| 22222 |        2 |            0 |        2 |
+-------+----------+--------------+----------+
2 rows in set (0.00 sec)


Max.