As services are rendered on the phone, the call manager release has very little to do with developing ip phone services.
Depending on how old your SDK is, you might have missed the introduction of a few new XML forms, but you can always use the latest ip phone services development guide from this page http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_programming_reference_guides_list.html
all the tags will also work on older ccm versions.
the only thing changing between call manager versions is axl, ldap (starting with ccm 5.0 there's no ldap on ccm anymore), and serviceability, but as long as you don't use any of those apis (and they really aren't part of the ip phone sdk anyway), you really don't have to worry about the sdk version.
I for one still use the 4.1.3 documentation to write apps for ccm 5.x.. it works like a charm.
