FIGURE 3: Potential call periods
username	potentialfrom	potentialto	rate
user1	2003-02-12 00:00:00	2003-02-12 07:59:00	.0200
user1	2003-02-12 08:00:00	2003-02-12 21:59:00	.0500
user1	2003-02-12 22:00:00	2003-02-12 23:59:00	.0200
user2	2003-02-12 00:00:00	2003-02-12 07:59:00	.0200
user2	2003-02-12 08:00:00	2003-02-12 21:59:00	.0500
user2	2003-02-12 22:00:00	2003-02-12 23:59:00	.0200
user2	2003-02-13 00:00:00	2003-02-13 07:59:00	.0200
user2	2003-02-13 08:00:00	2003-02-13 21:59:00	.0500
user2	2003-02-13 22:00:00	2003-02-13 23:59:00	.0200
user3	2003-02-04 00:00:00	2003-02-04 07:59:00	.0200
user3	2003-02-04 08:00:00	2003-02-04 21:59:00	.0500
user3	2003-02-04 22:00:00	2003-02-04 23:59:00	.0200
user3	2003-02-05 00:00:00	2003-02-05 07:59:00	.0200
user3	2003-02-05 08:00:00	2003-02-05 21:59:00	.0500
user3	2003-02-05 22:00:00	2003-02-05 23:59:00	.0200
user3	2003-02-06 00:00:00	2003-02-06 07:59:00	.0200
user3	2003-02-06 08:00:00	2003-02-06 21:59:00	.0500
user3	2003-02-06 22:00:00	2003-02-06 23:59:00	.0200
user3	2003-02-07 00:00:00	2003-02-07 07:59:00	.0200
user3	2003-02-07 08:00:00	2003-02-07 21:59:00	.0500
user3	2003-02-07 22:00:00	2003-02-07 23:59:00	.0200