1) you should be able to find out with the audit logs, time constrain from below also applies.
2) app logs and traces will have this info, but there's not going to be a "this is the 1st time this phone registers" message. They'll look exactly the same as if it was the 100th time it registers. Also, since this logs are nor permanently kept in CUCM, it all depends on how much info is stored whether you'll be able to find this for all phones or not.
HTH
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HTH
java
if this helps, please rate