Hi I have recently got a new HTC Desire S on O2. Several friends commented that when they tried to call me, they were diverted directly to voicemail - these were at times I knew my phone was on and had signal. I would like to point out at this stage I am by no means some technical phone wizard, but just wanted to share my experience for others who may be seeking an answer to the same issue... After trawling through forums to see why this could be, I thought I would share what I have found out following a massive internet search, some self-testing of the phone and subsequent calls to HTC customer service. It appears when you are connected to a 2G network (2G network/GPRS will be shown by a G and arrows next to the signal icon in the top right hand corner) and have your mobile internet connection turned on, and it is in use (or apps are using it in the background), you WILL NOT be able to receive incoming calls. I have tested this by switching off the mobile internet connection, and then calling my mobile. No problems - rings straight away. Then I have switched on the mobile internet connection (it was showing G i.e 2g connection as I live in a non 3G coverage area), and then started using the internet, and redialled my mobile - the call went directly to voicemail. I tried these tests several times, ensuring the phone had adequate signal each time, with the same results. I called HTC and they went through all the usual - changing settings, saying I needed a new SIM card (I am using a new SIM card already). I asked to speak to someone technical, who could explain the problem, as it was clearly a phone issue. Eventually I spoke to someone who admitted that you can not get voicecalls when using the Desire S internet on a 2G connection, the voicecall is apparently unable to interrupt the internet connection, hence why the call goes directly to voicemail. I have tested this with 3G and HDPSA connections (shown by 3G and arrows, and H and arrows, respectively, and there appears to be no issue - calls come through even if you were using the internet at the time. I can not comment for EDGE connections (E and arrows) though - as I rarely get this type of connection. Hoping this helps !