There are updates in AXL with new releases but most of them are additions -- so the existing interface doesn't change. For example, we have written a code to pull the phone list from CUCM via AXL for 5.x and it works without any problem with 6.x and 7.x as well. Cisco is getting better at making sure that the addition to AXL interface does not break the existing code.

Howerver, when it comes to JTAPI, you will need to use the same JTAPI jar as your CUCM and there are more inconsitencies. Even though JTAPI is mostly for call processing and AXL for administation, sometimes you can do the same thing either way. For example, to push to phone, you can get the phone list via AXL and use HTTP push without even using JTAPI. You can do a push via JTAPI as well.

We use only AXL and HTTP in our software so we don't depend on CUCM version as much. But there are things that only JTAPI can do and you don't have a choice -- like listening to call events.