Use popBackStack instead of creating a new fragment

src/org/linphone/AboutFragment.java

@@ -93,7 +93,7 @@ public class AboutFragment extends Fragment implements OnClickListener {
 					lc.resetLogCollection();
 				}
 			} else if (v == cancel) {
-				LinphoneActivity.instance().displayDialer();
+				getFragmentManager().popBackStackImmediate();
 			}
 		}
 	}

src/org/linphone/ContactDetailsFragment.java

@@ -253,7 +253,7 @@ public class ContactDetailsFragment extends Fragment implements OnClickListener
 			dialog.show();
 		}
 		if (id == R.id.back) {
-			LinphoneActivity.instance().displayContacts(false);
+			getFragmentManager().popBackStackImmediate();
 		}
 	}
 }