date range query help

Hi,

We have two tables.

select * from
mobile_custodian;

custodian_id | user_id | issue_date | return_date | mobile_no
--------------+---------+------------+-------------+-------------
4 | Ben | 2008-10-11 | 2008-10-13 | 09455225998
5 | Josh | 2008-10-15 | | 09455225998
(2 rows)

select * from
call;

call_id | datetime | mobile_no | charge
---------+---------------------+-------------+--------
2 | 2007-10-14 13:27:00 | 09455225998 | 5.2
1 | 2007-10-12 10:00:00 | 09455225998 | 4.5
(2 rows)

Now user Ben has passed his mobile to user Josh and we issued Josh his
mobile on 2008-10-15.

1. Is it possible for me to write a query that will have the fields

call.call_id,
call.datetime,
mobile_custodian.user_id,
call.mobile_no
call.charge

that will use call.datetime and lookup the date range from
mobile_custodian.issue_date and mobile_custodian.return_date to
identify the right user for each call?

2. Do I need to change the issue_date & return_date fields to
timestamp to perform the above?

Thanks.