I was thinking of doing the same. I also found a quite informative thread on here regarding this, but i cannot find it now. I just searched for 3 sim router but found nothing.
I was considering this as i still am unable to get fttc. my family use about 90Gb a month, which is too much data to use satellite broadband. I can see that a local company cotswold wireless have a 4g data tariff, but it is a tied in 2 year contract with quite a hefty installation fee.
I was thinking of buying my own 3g/4g receiver and installing it to some T&K brackets on placing it on the outside of my home, with a cable going into the router. Something like this ---> eBay item number: 271262303698.
I was thinking of having two tariffs at home, maybe keep my current broadband provider BT (i moved to them to get bt sport for free. I moved from sky, but my upload with BT is 448, whereas i had about 800k with sky) I think i may move back and attempt to get out of the contract with the upcoming price increase option. Anyway, i digress. So, i need an unlimited adsl line and another option with a decent upload and a fair amount of data for a decent price. My current adsl speeds is 4mb down & 448 up. My speeds with 3 mobile broadband in my iphone is 4Mb down and bout 1.5Mb up indoors downstairs. About 8-12Mb down and 2Mb up when upstairs. So hopefully when 4G is rolled out to my area next year, i was hoping that i would be able to use a sim and a wireless router. A 2 minute walk as the crow flies from my home i get over 20Mb speeds with 3.
I hope my local mast gets 4G. I am surrounded by fast broadband, but i just unfortunately cannot get any of it in my home.
Firmware: DD-WRT v24SP2-EU-US (08/19/10) std
BT Home Hub 4