First, after a long partnership with Infineon, Apple has decided to switch over to Qualcomm (the start had already been made on the CDMA version of the iPhone). So the iPhone4S now includes a baseband from Qualcomm, namely the MDM 6610, see this link.
The good thing about this, is that Qualcomm has historically made their diagnostic port available for various logging tools so we might finally get a closer look at what the iPhone gets up to. Maybe even a jailbroken version might make it available... Let's wait and see..
On the HSPA front, the E-DCH capability stays the same, namely 6, but the HSDPA category increases to 10. This in theory can support a maximum speed of 14.4Mbps. This however will utilise all the HSDPA resources in a cell and will require perfect radio conditions (14.4Mbps requires 1:1 coding i.e. no redundancy) so in theory what users will get is much less.
On the antenna front, the iPhone4S supports Rx diversity, which although wide spread for mobile broadband dongles is still rare on handsets. This should improve performance over the older iPhone models considerably. There are also rumours that the iPhone4S also supports Tx antenna switching, where it can switch between the two antennas depending on which Rx antenna is receiving more energy. The author has not been able to verify this though.
Finally, the iPhone4S is also CPC (Continuous Packet Connectivity) capable. Specifically it is capable of supporting the Rx DTX and Tx DTX aspect of CPC. This means (in simple terms) that it can shut off its transmitter and receiver when not transmitting/receiving data thus saving battery life. Early indications show that this capability is not enabled at the moment but once Apple it is happy with its performance on some live networks it will probably enable it through a SW update.
Perhaps the only disappointment is that it doesn't support WB-AMR, which for a phone of its class is something I personally believe Apple should pursue.
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