The MS system for activation of OEM builds is fairly lax - and often Telephone Activation will work so long as certain (unpublished) conditions are met.

It's my belief that the following are (some of) the conditions that must be met for OEM_COA_SLP Keys to work on transfer to a new computer:

  • If the COA Key has never been used, then activation will proceed normally (ALL COA Keys require Telephone activation the first time they are used!)
  • If the COA Key has only been used for activation once, then so long as there is at least 120days since that activation, then it usually works on telephone activation
  • the more activations, the more likely you are to have to speak to an operator and explain yourself!

For System Builder Keys, then the first doesn't ever apply, since the Key will have been used since first install :)