Ask yourself a couple of questions to save yourself a lot of money:
1. The minimum capacity for an iPhone is 16GB nowadays (iPhone 4); an app is usually like 15MB on average (120MB at most if you got some crazy a.ss game), photos are like 1MB at most... how many apps and photos do you really need that you need 16GB just for that?
2. The music pauses when you make a phone call and resumes when you end the call. If you're calling someone, why would you be playing music anyway during the call?
I used to have an iPod Touch until I got my iP4 -- sold the Touch, now my iPhone is in charge of most of my life: music, email, contacts, networking, web, etc.
My hunch is that this is gonna be the 4S, not the 5, so don't get y'all hopes up. They're probably gonna drop the 4S with iOS5, test out all the kinks and bugs with the iOS, fix 'em, then release the iPhone 5 probably next summer with iOS5 pre-installed.
Unless its business, I leave my music going while I talk on the phone especially if i'm vibing. I'll turn it down but it will keep playing. Thats why I said I have to have two separate devices. Besides I have multiple ipods loaded with a genre of music for how I'm feeling that day.
I think I'll stick with separate devices and maybe check the iphone 5 after all the bugs get worked out that you spoke of.