Play 1, iPhone creating wireless network, no router

You need something to create the wifi network. If you use your phone for that you cannot use it also as a controller or play the music stored on it. You could use the iPad to control and play the music on the iPad.
If you want to use both you need something else to create the network. That could be anpther phone, a travel router or even a conventional router if there is no wish to connect to tbe internet

The one I linked above has USB port for drive as well. The trek John noted is a very highly rated one but more expensive.

Sorry, I was under the impression the travel router would create the non-internet network that the Play1 could connect to, then the iPhone would stream the music via the wifi.

No travel router grabs the wifi off the iPhone and uses it for internet. Then the travel router creates a new wifi network working exactly like your home wifi network. You could even give it same ssid and password as home network and Sonos would think still at your home.

Sorry, I was under the impression the travel router would create the non-internet network that the Play1 could connect to, then the iPhone would stream the music via the wifi.This is in fact correct, and I thought is what I said in my previous post, and I have used the travel router like this. What Chris is describing is the more usual use for a travel router, however.

With the non internet network your iPhone could only stream music residing on phone. No internet streaming.