There is already a WiFi access point, router or gateway in every house these days and you don't need to change your current system setup. All you need is a WiFi-Ethernet bridge to connect it to an Android phone like this:
Usually a phone's WiFi power is not strong enough to get your house fully covered. This is pretty much the #1 reason to use a bridge and a normal WiFi router other than just the phone as a hotspot.
Furthermore, there is no wire between the phone and the bridge; so you can put the phone at the best spot for the best reception possible in your house. Mobile data speed is hugely related to the signal level; the better the signal, the faster the speed especially uploading.
Usually an Android phone is limited to allow only 5 to 10 devices. This comes to another big benefit of using a bridge: such limit is entirely removed by the bridge. The phone's built-in hotspot won't see any device connected to it. Note: this "feature" may not apply to a third-party hotspot app such as WiFi Tether Router.
The bridge I use is a Linksys WET610N, a used one cost about $15. It has been working perfectly for more than a year now. The only glitch is: I must use WPA instead of WPA2, otherwise it disconnects and reconnects to the phone every now and then. I think this issue has something to do with WPA2's periodic key renew scheme.
You can easily switch back and forth between this newly added wireless connection and your old broadband. You don't need to change WiFi password on your devices, they connect automatically to either. So this is also a good way to add a backup to your existing broadband, not necessarily a replacement.
I have tried some 3G routers including MiFi in the past, none of them worked well. They are incompatible to many phones and dongles and they are not reliable and dependable. My above phone + bridge + AP system almost never need a reboot for weeks after weeks. An Android phone is also far more flexible, you can do many things on it, such as VPN.
