Upgrade to squid3 and block mobile carrier uniquely identifying headers:

# Mobile carrier uniquely identifying headers
request_header_access MSISDN deny all           # T-Mobile
request_header_access X-MSISDN deny all         # T-Mobile
request_header_access X-UIDH deny all           # Verizon
request_header_access x-up-subno deny all       # AT&T
request_header_access X-ACR deny all            # AT&T
request_header_access X-UP-SUBSCRIBER-COS deny all
request_header_access X-OPWV-DDM-HTTPMISCDD deny all
request_header_access X-OPWV-DDM-IDENTITY deny all
request_header_access X-OPWV-DDM-SUBSCRIBER deny all
request_header_access CLIENTID deny all
request_header_access X-VF-ACR deny all
request_header_access X_MTI_USERNAME deny all
request_header_access X_MTI_EMAIL deny all
request_header_access X_MTI_EMPID deny all