Opting out of the CRAs is very important, IMO, prior to apping for a mortgage. It stops the CRAs from providing your credit info to CAs if they subscribed to your CRs. So, if you app for a mortgage, they won't get alerted to that app if opted out. It's very common in the Mortgage Loans board to see that last second surprise CA pop on in the middle of someone's mortgage process. CAs know that if they report, your lender might require you to pay it prior to closing. Opting out in no way prevents CAs from reporting, it just makes it harder to get info that can trigger their reporting.
If you pull your CRs directly from the CRAs, you'll see a section for soft inquiries. Some of these inquiries are labled "PRM" for promotional. Opting out prevents companies like CCCs, insurance companies, etc. from getting your info. While it is still possible to get preapprovals while opted out, you aren't likely to get preapprovals from companies you don't do business with already.
Now your existing creditors will often pull a soft called a "AR" or account review. In that soft, they can still see your report while opted out and some can even extend offers of credit. Some do not. I had a preapproval notice from BofA. When I opted out, that preapproval disappreared within a week and never reappeared despite having better credit. On the flip side, I still got an occassional preapproval from existing CCCs while opted out. YMMV I bet. On the flip side, while opted out, I even got preapprovals from companies I did not do biz with, but these were junk cards like First Premier.
Since you did it over the phone, I would pull your full reports from the CRAs (or annualcreditreport) to be sure. It'll have an opt-out nitice towards the end of the report.
BTW, I recently opted back in once we cleared our mortgage and the flood gates opened on junk mail, insurers, etc. Sure enough, there were over a dozen companies sniffing around the past couple of months on my and DW's CRs.
I never heard of opting out with existing creditors.
