-- таблица телефонов

create table tel (
 id int not null auto_increment,
 phone varchar( 20 ),
 primary key(id));

insert into tel (phone)
 select '+7 900 100 00 01' union all
 select '+7 900 100 00 02' union all
 select '+7 900 100 00 03' union all 
 select '+7 900 100 00 04' union all
 select '+7 900 100 00 05' union all
 select '+7 900 100 00 06' union all
 select '+7 900 100 00 07' union all
 select '+7 900 100 00 08' union all
 select '+7 900 100 00 09'

-- таблица персон

create table persons (
 p_id int not null auto_increment,
 name varchar( 20 ),
 id int,
 primary key(p_id));

insert into persons (name, id)
 select 'Вася',  2  union all
 select 'Петя',  3  union all
 select 'Boss',  1 

-- занятые телефоны

select p.name, t.phone
from persons p, tel t
where p.id=t.id

-- свободные телефоны


select t.id, t.phone
from tel t left join persons p
on t.id=p.id
where p.id is null

+----+------------------+
| id | phone            |
+----+------------------+
|   9  | + 7   900   100   00   09  |
|   8  | + 7   900   100   00   08  |
|   7  | + 7   900   100   00   07  |
|   6  | + 7   900   100   00   06  |
|   5  | + 7   900   100   00   05  |
|   4  | + 7   900   100   00   04  |
+----+------------------+