netgear wdnr3700 as a wan bypass mode with att uverse 3801hgv???

Hello rom,

There is a great guide that may help you here. 

Previously Discussed Set-Up (Set-Up I)
For a residential set-up, yes. This is perfectly fine and it's the best way you'll obtain the coverage you want, with the technology you want (Wireless N), without sacrifcing speeds as much. Wireless repeaters, another option, but carry their own limitaitons (Alternative Method 2 below.) 

Limitations of Set-Up I
There are a few limitations to note, though. A) While the access points are capable of delivering link speeds up to 600Mbps (300+300), Fast Ethernet is a limiting factor here. The 2Wire 3801 is only Fast Ethernet capable. So your maximum link is substantially reduced to a maximum speed of 100Mbps. (Which is perfectly fine for internet purposes since your connection is well below 100Mbps, and streaming within your LAN should be adequate, however transfer speeds will not be the maximum available speeds.You'll notice this more if you're doing File Transfers within your network, such as to/from a NAS server.) B) Any 5GHz connections, and Wireless N will downgrade to 2.4GHz Wireless G if you leave WNDR3700 coverage into your RG's coverage area, and in some rare* cases may drop momentarily. (*Rare - based on my own personal experience.)

Solution to Limitation B.

You can potentially eliminate the chance of the latter, by disabling the wireless setting of your RG and using the WNDR3700's for wireless connectivity. (If range allows.) You'd then be operating 1 Wireless Network using two Access Points, rather than three. Your residential gateway would still handle all routing duties. 

Alternative Method - Seperate Wireless Network (Set-Up II)
(Solution to Limitations A and B of Set-up I)
You can partially eliminate the speed limitation by creating a seperate network rather than extend your current one. (Although this in itself would create other limitations.) In this case on of your WNDR3700s would be set in router mode, and the other WNDR3700 would be set as an access point. You would turn off the wireless functionality of your Residential Gateway. In this set-up the devices on your LAN would be able to communicate with wireless devices at up to maximum Wireless N speeds, and among wired connections up to 1 gigabit. If you setup your router in DMZ+, your Chromecast, and other devices will be able to use UPnP.

Limitations of Set-Up II
You will be on a different Subnet than your Residential Gateway, so your wireless devices (and any devices wired to the WNDR3700) will not be able to communicate with your U-Verse Devices (No U-Verse enabled Interactive Apps) nor will you be able to watch Live TV using the U-Verse Apps or U-Verse.com on those devices.

Alternative Method 2 - Using a Wireless Repeater/Wireless HomePlug Adapter (Set-Up III)
This isn't what you asked for, but it is an available option. This is by far the easiest set-up. All you'd have to do is sync your Wireless Repeater to your Residential Gateway or connect the HomePlug adapter.

Limitations of Set-Up III
Involves purchase of additional equipment. Wireless repeaters are typically placed near the edge of a wireless network and will increase your range a bit, but they are limited to the incoming link speed. (ex. Hypothetically, if your repeater's incoming link speed is 10Mbps, your repeater will only be able to use that 10Mbps for all devices that connect to it.) In set-ups I and II, the network link is acheived by ethernet cabling, rather than wireless. HomePlug adapters use your existing electric wiring. Due to this, they are limited to internal wiring. (This can cause them to not be able to communicate with each other.) Their speeds are also usually lower than set-ups I and II.