You'll find more info on internship and residency in the osteo and residency forums. More reliable there too: we're premeds here.
But, having done some obsessive research, here's my understanding. A DO grad who might want to practice in Florida can either:
1. Do an AOA residency in which the first year is pre-approved as the traditional rotating internship. Some, not all, AOA residencies are integrated as such. (A very very small number of AOA residencies are dually-accredited with ACGME residencies, btw, and a subset of these integrate the TRI.)
2. Do an AOA residency AFTER doing an approved TRI. The TRI may or may not be at the same institution as the AOA residency. The AOA residencies that assume you've completed a TRI are generally a year shorter than the ones that integrate it, but not always. (Note that the number of residency years varies by program - you'll see research years at some programs and not at others, for example.)
3. Do an ACGME residency AFTER doing an approved TRI. Worst case. However, in some cases you could theoretically get your TRI counted as your first year for an ACGME program that requires a separate intern year (not that I can think of any such cases off the top of my head).
4. Do an ACGME residency, apply for a rule 42 to get your first year approved as a TRI, and do required OPP flag-saluting presentations at AOA conferences. Rule 42 varies greatly by specialty, and you should look on do-online.org for the per-specialty required rotations during internship. If you're doing FM or EM, the list of required rotations for the AOA closely matches what you'd do in an ACGME residency anyway. The AOA requirement of months of IM in a general surgery residency, on the other hand, isn't met at any ACGME gen surg residencies.
5. Military. I don't know jack about these.
What I recommend is getting familiar with some specific residency programs that you are likely to be interested in. For example, you could pick Christiana Care in Delaware, which has ACGME and AOA residencies and an AOA TRI. Dig into the department pages and see what the actual expectations are at this institution, and then you can use what you learn here to figure out the next institution.
Best of luck to you.
