DataUsageSummary: fix mobile data usage display for sim-less devices

- Don't assume the device has a sim card. Check for a phone number
  instead. Otherwise the mobile data usage screen will not show up
  on sim-less CDMA devices.

Change-Id: Ic6e35dc209ff05e0c89dc990ad82f4ab4d3f337d
Merge "DataUsageSummary: fix mobile data usage display for sim-less devices" into jb-mr1

Change-Id: Ib6c3349a3e3e9041e3e612f43219b9a0ee495b54