Looking for a Wi-Fi Router that works with Cellular Aircards

I have a Sierra Wireless 881U USB Aircard that I use with AT&T's 5GB/month data plan. It works well now since I just use it on a couple laptops I have but now that I'm buying an iPad I want to avoid an extra $30/month for data and just share the data plan with it. Since the iPad doesn't have USB that means I'll need a solution to use Wi-Fi on it.
I came across the Cradlepoint PHS-300. It's nice since it has an internal battery or can plug in and is fairly small and I simply plug in my aircard to make a local wi-fi access point that I can use on the go with either my laptop or iPad.
My question: Are there other options on the market? Cradlepoint makes some others but they don't have a battery. I want one with the most battery life for the smallest sizes and have been unable to find any from Linksys but are there other items like this on the market?

Also, another question. I'm happy with AT&T's data plan but my contract is up shortly. Does anyone have opinions of Verizon or Spring or even T-Mobile? I don't know much about T-Mobile and it seems like Verizon's plan is similar and even Sprint's current 3G plan is similar. it seems once 4G is available in an area though for the same price of $59.95/month you get unlimited data. that sounds too good to be true and is it really true and is the service and speed good?

Thank you for your help with the above.

I have the PHS 300 and it works quite well. I have a smaller battery than this and it extends the life pretty well. This one looks like it will last most of the day.
Battery Pack for 3G Routers (CTR350, PHS300, CTR500, MBR1000, KR2 and Pepwave Surf Mini) [MP3450i] - $189.95 : 3Gstore.com, Mobile Broadband Made Easy. CradlePoint Routers, MiFi, Antennas, Amplifiers and Verizon & Sprint EVDO Modems.
Ypu'll notice other routers that can run on battery - on the same page. I can only vouch for the PHS 300.

I have a mifi so I tend to use that plugged into the battery just so my internet lasts longer. I use the PHS 300 usually when I'm somehwere I can plug it in.

I have an iphone and I have verizon data. I think it is very area dependent but my experience is that for data Verizon has better coverage for where I travel. YMMV. Sprint always seems to be the first to deploy the fastest wireless - but right now it is only in 10 cities. None of which help me. I guess if you wanted to future proof that is your best bet currently. Otherwise I like Verizon's data.

Cradlepoint is the way to go.
Also, check out millenicom.com. For $60/month you get 20G/month and no contract necessary!