Perfomance problems - Mailing list pgsql-admin

Hi

    I'm building an app (A) that inserts about 30.000 - 40.000 records in a
table per day. Another app (B) get this records and process it, an then
the records are deleted.  The A app gets 50 records each time, this SQL
statement takes 10-15 seconds. I make a vaccum and the time is now about
5-10 seconds, bu it's to slow. It enqueue records, about 10-20 in each.
The B app takes less than a second in process each message.
    The statement is
    SELECT * FROM table_a
    WHERE number = 123
        AND msg_orig = 'A'
    ORDER by id;

The table is:

    id serial primary key,
    data varchar(260),
    number varchar(12)
    time_a timestamp,
    time_b timestamp,
    msg_orig varchar(3)

Indexes:
    Number,msg_orig, id, time_b

Please, Help, What I'm doing bad?
I'm using 7.1.2 in Solaris.

Thanks.