I moved to a remote section of Chiang mai and won't have proper Internet connection for about three months. I've been using my iPhone as a hot spot and it's marginally successful.

If I buy a ais air card which works on 3G can I use it when I want and disconnect when I want or is there an expiration date I.e. must it be used in a month or can I carry it over when I need a faster connection

Or is there another solution all together

Most decent, volume-based, unlimited, full speed mobile data plans run for one month, and recur automatically. One cannot hoard/save "bandwidth volume" for use over a period longer than 30 days.

I do not understand why an aircard would be necessarily better than using your iPhone as hot-spot? Assuming you have AIS/2100 MHz 3G coverage just use an AIS SIM, subscribe to a mobile data plan and enjoy. Or try a TrueMove H SIM.

But then maybe there is more to the story?

As always, sharing as much detail as possibile - what is the iPhone model, what kind of SIM -plan/promotion do you have now, what does "marginally successful" mean in this context?, etc. etc. etc.can lead to more focused recommendations.

My iPhone 5 works well as a hotspot until my capacity 3mb runs out then it's slow. Can I up my contract to 6 or more

Guessing here: you have an AIS/2100 MHz SIM, prepaid, 3 GB monthly plan?

Think you can go up to 4 or 5 GB plans. Just about everything here has a fair-use speed limit, once you reach your cap, which varies from 64 Kbps to 384 Kbps.

http://www.ais.co.th/3g/th/smartphone-package.aspx?package=Extra-Package#tips

You may also be able to cancel an existing plan once you reach your cap, then re-subscribe to another plan.

Brilliant thanks

Other option might be dtac

The dtac plan of 7GB @ 999baht is 142.7baht per GB and topping adding of 1 GB @ 150baht ea. Almost the same as the package price so just top up what you need when you start to get short.

http://www.dtac.co.th/en/postpaid/products/aircard-tablet-unlimited.html

Other option might be dtac

The dtac plan of 7GB @ 999baht is 142.7baht per GB and topping adding of 1 GB @ 150baht ea. Almost the same as the package price so just top up what you need when you start to get short.

http://www.dtac.co.th/en/postpaid/products/aircard-tablet-unlimited.html

TopUp on a PostPaid plan?

Other option might be dtac

The dtac plan of 7GB @ 999baht is 142.7baht per GB and topping adding of 1 GB @ 150baht ea. Almost the same as the package price so just top up what you need when you start to get short.

http://www.dtac.co.th/en/postpaid/products/aircard-tablet-unlimited.html

TopUp on a PostPaid plan?

As far as I know you can add 3g air volume to a post paid plan - I run two cards and have yet to have to buy it with 7 GB, but right on my landing page is the option, price and suggestion that I do and link.. They even say something about topping is used first over reg air volume.

The dtac plan of 7GB @ 999baht

Yeah, that's a post-paid (contract) plan, and given the temporary nature of the OP's requirements (3 months) this may not be an option.

But yes, you can "power up" a post-paid plan with DTAC: http://www.dtac.co.th/en/postpaid/products/addpack-internet.html