Just because your practice has been purchased by the hospital doesn't mean you'll definitely be doing provider based billing.
Check to see if you'll be billing under a separate physician corproation TIN, in which case you'll be billing as if you were a practice.
If your practice is going to be considered a department of the hospital, and billing under the TIN of the hospital, then you will be doing "provider based billing", which means you submit a professional fee charge on a 1500 (same as you do now), and a corresponding technical charge/facility on a UB for government payers.
You'll have to set up your criteria for the technical charge, which is usually a level visit based on the nursing resources used for the visit. That's what is billed on the UB. For your 1500, you'll bill your usual E&M and your POS will be outpatient hosptial (your "office" is now considered POS 22). Surgeries will be billed out as they usually are, because they're done in the hospital facility, and those technical charges are unrelated to the "office", but office procedures will be done with both a professional and technical fee in the new "outpatient department".
There are pros and cons. Of course there is the increased revenue for the provider-based billing...but your Medicare population will now get two bills for what used to be an "office visit". Your staff will need to have devised some very good scripts to communicate this to the patients, because your billers will get a bazillion calls at first. Eventually, it irons out, but it's a lot of extra work if your billing systems don't allow you to "split" bill without having to post two sets of charges for each service.
Does this help?