Can I call or drop-in on other Echo users from my Reason Clock?

No, the Alex Comms functions (i.e., Call, Message, Drop-In, and Announce) of Amazon Echo devices are not supported by the Reason Clock at this time. But, we are working to add these functions. There's no definitive release date for these additional functions. Should we be successful in our effort, we would push out a firmware update via OTA.