This is my OK code in QT 4.7:
//add combobox list
QString val;
ui->startPage->clear();
val = "http://www.work4blue.com";
ui->startPage->addItem(tr("Navigation page"),QVariant::fromValue(val));
val = "https://www.google.com";
ui->startPage->addItem("www.google.com",QVariant::fromValue(val));
val = "www.twitter.com";
ui->startPage->addItem("www.twitter.com",QVariant::fromValue(val));
val = "https://www.youtube.com";
ui->startPage->addItem("www.youtube.com",QVariant::fromValue(val));
// get current value
qDebug() << "current value"<<
ui->startPage->itemData(ui->startPage->currentIndex()).toString();