This one had me scratching my head for a while. Mac is a MacBook Pro running mountain lion 10.8.3.
When you plug in the dongle a new Location is selected in the Network pane of System Preferences. This does not have Wifi included as default so your wifi will be disabled. Go to the Network pane and click the little “+” and add in WiFi. Head to the Sharing pane of System Preferences and click Internet Sharing on the left. Choose the modem “Huawei something or other” from the drop down list and tick the Wifi boxes underneath. Choose Wifi Options to set the wifi network name and password. Tick the Internet Sharing box to cofirm and turn it on.
Then from your other devices simply connect to your new wifi network 🙂