We've given it a go, but we use SSL to connect to the provisioning server which creates headaches for the SPA122/112.
From what we could gather, if you're using SSL then you need to send Cisco the SSL csr and key and they provide a CA file that can be uploaded to the 122/112 device so you can connect. It was a few months ago, so my recollection is a bit hazy.
We're not using a self-signed cert, but it seems cisco strip down the CA's in the unit