Apple will tie this into their normal AppleID system. You could put 50 credit cards on it, it will be three free months per AppleID account. If you want to game it to get three months of free streaming music...good luck there. It's not just web form, AppleID also ties in the devices too. Your "new ID" for that "free streaming music" won't have access to your regular Itunes, messages, cloud storage, installed apps, etc. You'll have to log out of your regular account and sign into your new one. If you screw it up, you might even loose access to your Apple device itself.
Whomever is suggesting this as a course of action must not have any experience with the Walled Garden. I don't actually use Apple products personally, but I've been forced to support them for several years at work. The best / funniest support was a woman freaking out that her boyfriend had "hacked her phone", not realizing that everyone using the same ID across multiple devices will have access to everything like that. It's a feature of the OS...the Apple support chick and I laughed about it for awhile before she took over the client to help them "separate" it all into their own accounts, or maybe get some relationship counseling, I don't know lol.