Future changes to the 1500 form may be released in the next few years, however in the short term Medicare has released the following dates which will transition to using the NPI.
1/1/2006 - 10/1/2006 - PIN or NPI numbers will be needed on the 1500 forms however NPI numbers alone won't be accepted.
10/1/2006 - 5/1/2007 - NPI number transition. Claims could be denied without the NPI.
5/1/2007 - NPI manditory. Claims will be denied without NPI.
To apply for the NPI number Medicare has setup the following website: https://nppes.cms.hhs.gov and is free of charge.