If a new calendar year cash balance plan is established with a 1-1-2009 effective date, can the crediting rate for the cash balance accounts (not the funding rate), use a rate in effect at the beginning of the plan year (such as a rate for the month of January), or must the plan have a 1 month (or more) lookback to get the crediting rate (such as December's rate, or August's rate)?

Maybe this is clearer, could a plan define it as the rate of interest on long-term investment grade corporate bonds (as described in Code Section 412(b)(5)(B)(ii)(II), such code section as it existed prior to amendment by the Pension Protection Act of 2006) determined as of the first day of the Plan Year for which the Interest Credit shall be applied?

If it's a calendar year plan, would that be the January rate, or December's?

I think this would be fine. There is no required look-back for this purpose (interest credit) like there is for 417(e) purposes, which no longer applies to cash-balance plans anyway. I see no problem with this.