Partitioning table and dynamic SQL in trigger

In our DB we create partition table for each month (our naming
convetion is follow , and I would like to create trigger that insert
data to appropriate partition table accounting.cdr_y2009m05,
accounting.cdr_y2009m06 etc..).

What is the best solution to create such trigger? I can create trigger
function as follow:

CREATE OR REPLACE FUNCTION partitionig_test RETURNS TRIGGER AS $$
BEGIN
IF NEW.effective_date>=DATE '2009-05-01' and
NEW.effective_date<DATE '2009-06-01' THEN
INTO accounting.cdr_y2009m05 VALUES (NEW.*);
ELSE IF ....
...................................

but in such solution every month I have modify trigger to handle new
month (during import I have to remember about archive months). Second
solution is to create dynamic SQL query, but every call of
partitionig_test I have to build long string - accounting.cdr_* table
has 50 columns.
Maybe you know third solution, most elegant ?

Michal Szymanski
http://blog.szymanskich.net