Depending on the mobile network provider you use (MTN doesn’t seem to be affected in ZA at the moment, Vodacom in ZA leaks this information), and device used, your IMEI and MSISDN (mobile number) are being sent to each web server you access via the mobile data network. In addition, tracker headers are being added.
You can see this here: http://blog.sven.co.za/sniff/ (access the page from your mobile phone on 3G/4G/GPRS or EDGE). Depending on the phone and network you’re on, your IMEI number uniquely identifying your device, mobile number as well as some injected X-ACR beacons are injected. The bearer type and internal network IP on the Cellular ISP’s network are also transmitted.
Solution: Browse via a proxy of your own control, or VPN.
Or switch mobile provider.
But you knew that already.