I had Progressive on my older '94 Bounder and mistakenly thought I'd get a discount when I added my newer '02 Winnie. After all, I could only drive one of them at a time. But no discount, I discovered after paying up front.
I'd called them, expecting to get a couple questions asked, and I'd assumed I'd get a multiple policy discount. The salesman told me yeah, I was getting their discount. When I looked into it, turned out the guy was less then honest. They'd added a premium onto my two policies of around $225 or so over if I'd bought the 2nd policy separately online. Salesman's commission I'd wager.
Cancelled both policies. Cost me $60 to do that too. Came back a month later and bought just one policy online (and I'd sold the Bounder so didn't need a double). Still saved money over buying over the phone.
So I'd recommend you check for a policy quote online, do not mention you've got a policy with them (they ask that on the online form). At least with Progressive. I'd bet this is true for all insurance companies these days though.
If you call and talk to a real person, it's gunna cost you.