Hi. Just wanted to share my (frustrating) experience with ordering a Sub on backorder.

1. On 3rd of February I order a Beam and a Sub. Beam is in stock, am charged for it instantly and it gets delivered on time.
2. Sub is put on backorder for 12th of February.
3. On 11th of February I receive an email saying Sonos was unable to charge my card due to some issue on THEIR side. They suggest calling support.
4. I call sales support. My previous order is cancelled. New is created on my behalf and I will now have to pay for an invoice via bank transfer. I am promised that my location in "backorder queue” will be kept and I will not need to wait for weeks+.
5. As you can imagine, order is created - estimated delivery 19th of February (so I have lost my backorder queue, irregardless to what the sales rep said).
6. I have to call again later that day to receive the invoice (although 1st sales rep said it'd be sent asap).
7. I receive invoice, pay for it immediately. No email confirmation for 1 day.
8. Next day I call again, get a confirmation that "payment received, we can release”.
9. The order status on web page > Orders page has still not changed from "New” to "Paid” or something like that. 

Basically, be ready to get disappointed every step of the way if you order something that's out of stock at that point. And forget paying with cards in EU, since that - apparently - frequently fails, as per 2 sales reps confirming it. Pay with Paypal or something instead.