Query that calculates the number of simultaneous calls

I have a MySQL table that has call records. Using the connect date/time, disconnect date/time and duration fields. I would like to be able to calculate the number of simultaneous calls that occurred hourly or daily. Below is an example of the values. The duration value is in seconds.

+---------------------+---------------------+----------+
| connect_time | disconnect_time | duration |
+---------------------+---------------------+----------+
| 2012-10-17 10:00:01 | 2012-10-17 10:05:30 | 329 |
| 2012-10-17 10:00:03 | 2012-10-17 10:00:32 | 29 |
| 2012-10-17 10:00:04 | 2012-10-17 10:00:38 | 34 |
| 2012-10-17 10:00:10 | 2012-10-17 10:05:29 | 319 |
| 2012-10-17 10:00:10 | 2012-10-17 10:29:19 | 1749 |
| 2012-10-17 10:00:11 | 2012-10-17 10:00:49 | 38 |
| 2012-10-17 10:00:12 | 2012-10-17 10:00:44 | 32 |
| 2012-10-17 10:00:12 | 2012-10-17 10:05:41 | 329 |
| 2012-10-17 10:00:13 | 2012-10-17 10:00:37 | 24 |
| 2012-10-17 10:00:15 | 2012-10-17 10:00:38 | 23 |
| 2012-10-17 10:00:15 | 2012-10-17 10:22:12 | 1317 |
| 2012-10-17 10:00:16 | 2012-10-17 10:01:32 | 76 |
| 2012-10-17 10:00:17 | 2012-10-17 10:01:08 | 51 |
| 2012-10-17 10:00:20 | 2012-10-17 10:00:54 | 34 |
| 2012-10-17 10:00:21 | 2012-10-17 10:00:59 | 38 |
| 2012-10-17 10:00:22 | 2012-10-17 10:00:34 | 12 |
| 2012-10-17 10:00:23 | 2012-10-17 10:00:28 | 5 |
| 2012-10-17 10:00:25 | 2012-10-17 10:04:09 | 224 |
| 2012-10-17 10:00:26 | 2012-10-17 10:00:29 | 3 |
| 2012-10-17 10:00:26 | 2012-10-17 10:22:13 | 1307 |
+---------------------+---------------------+----------+