Question, if you unlock an AT&T phone, do you still have to wait for updates to be released by AT&T or you can get them directly from MS as for example a 1520.3 does. Thanks
The current unlock status of a phone does not affect the update source.
That is dictated by the phone's firmware. An ATT phone with an ATT ROM means it will get updates from ATT regardless, whether unlocked or not.
Flashing it to, say, an international ROM will not unlock the phone, but it does change the update source to be direct from Microsoft/Nokia.
Example: My 920 is AT&T locked, but flashed on a French ROM. (complications led to LTE loss, but if I had more time, i might put in the effort to fix it.) meaning updates are unimpeded.
If your friend buys it now, they'll probably have to pay for a few months of service, so don't do it. Buy unlocked, that will be easiest.