We have an Advance II modem that we can plug into an external aerial 3G/4G
http://www.gadgetguy.com.au/product/telstra-wifi-4g-advanced-ii-netgear-aircard-790s/
My Iphone has more data that I use 16Gb / month shared with my wife and so for $5 per month I got an extra sim that goes into the Advance II and shares the 16Gb. If we get close to the 16Gb when travelling ... we can put in a normal prepaid sim till the 16Gb refreshes ... but this rarely happens.
The Modem above, on an aerial, gives us much better distance/speed under the same conditions as the Iphone being used as a hotspot.
Cheers
John