Find Phonecall Records Based On User At The Time Of Call

i have a table of phonecall records detailing amongst other things the time and duration of the call. there is a relationship linking this table to a table of handsets and from there to a table of users. this users table lists the start date the user had the phone. as ever sample data might make this easier to show:

PhoneUsers table

PhoneUserID Name StartDate PhoneID

1 john 1/08/2006 1

2 bob 20/08/2006 1

3 fred 2/08/2006 2

etc

Phones table:

PhoneID

1

2

etc

PhoneCalls table:

PhoneCallID PhoneID CallDate Duration

1 1 10/08/2006 25

2 1 23/082006 20

3 2 23/08/2006 20

i want the following result set:

user calldate duration

john 10/08/2006 25

bob 23/08/2006 20

fred 23/08/2006 20

essentially i am trying to link the phonecalls to the user of the phone at the time of the call. i make the following assumptions regarding the data:

the user is responsible for all calls for a given handset from the 'startdate' until the next 'startdate' for a different user, if such a record exists, if not then for all calls after that date



thanks