Notify user regarding invalid number during MO call.

When user dials an invalid number, network returns an error indicating
"unobtainable number" (See the Table 10.5.123/3GPP TS 24.008 for
the possible failure causes). Changes done to display message to
indicate user that an invalid number has been dialed.

Change-Id: I477d64bc3b59cc205396f911ff9630c640f619f3