Isn't that the exact reason of having radiant barriers, to prevent the use of Cell phones or other wireless devices within the realm of those barriers?

They have the radiant barrier installed to keep their electric bill lower but didn't realize this would be a side effect.

If you need wireless connectivity in such an environment you will only be left with distributing access points  at many locations. For Cell Phones I'm afraid I don't know what you could do (maybe there is some antenna you could run outside the house, with some kind of relay equipment to distribute the signal inside the house). Usually the insulating material has a reflective aluminum coating, and that effectively blocks electronic signals.

I didn't think 2 routers would do it.  I was thinking of multiple access points as well but he insisted that this would work.  I had to bite my tongue on his insisting the multiple routers would work (a buddy told him it would) because he hired me since he couldn't get it to work.... but I want to make sure before I go buying a bunch of equipment that putting boosters or access points would work.  It is one of those 2 story mcmansions and as far as I can tell there are so many walls and hallways that we may have trouble even with multiple access points.  The house is completely wired but he insists he wants hot spots in all rooms of the house for his wife to take her laptop whereever she wants to.  

I ended up adding an access point downstairs and using 1 router.   The 1 room we couldn't get the signal to, he decided to use the wired connection only in it.

They do make cell phone bi-amplifiers, but you need to know what frequencies they're using. There are some dual-band cell phone bi-amps (aka repeaters), but I don't know of any affordable units that cover all cell phones.

The general way they operate is, you mount an antenna outside connected to the inside unit via coax. It brings the signal inside and rebroadcasts it, then the inside unit picks up the signal from the cell phones and rebroadcasts it through the outside antenna back to the tower.

See diagrams here - http://www.wilsonelectronics.com////Products.php?Type=B

Here's one that works with all providers except Nextel's iDEN - http://cellphoneboosterstore.com/products/yx-610-dual-band-for-large-homesoffice-in-10000-sqft-range/

Here's a couple that are supposed to work with Nextel
http://www.criterioncellular.com/repeaters/nextelrepeater.html

http://www.cellantenna.com/repeater/cae50nxt.htm (top 2 on that page)

I'm actually surprised the providers don't sell those units at their stores/kiosks, themselves.

One thing I'm not clear on... are you saying the radiant barrier was installed in the interior walls, too?