Well, your data needs for those 2 months is rather high, considering you will be using a hotspot coupled with a mobile plan.
If you need that much data, but not 4g speeds, you likely can just use the prepaid 60 dollar a month plan.
I have no idea why, but my throttled(after my monthly allotment of high speed 4gig of 4g data limit)speeds are very fast.
I have no idea why, but it sometimes will get down to kinda slow, but I can still surf the web, downloads small files, etc, and do all the email I want. Then at times, it's as fast as my fone can handle. My 4g speeds would be faster if my phone was better, but I'm on a very cheap fone, so my hotspot speeds are kinda slow to begin with.
BUT, it's faster then my monthly plan for wifi with the citywide wifi paid service. SO, I am using my att phone as a hotspot and it's my only source for internet.
SO, I'd say, either call ATT and try to get a "short packaged deal" for 2 months that's not too high priced according to what you can afford, or just spend the 60$ and use the unlimited plan with your hotspot.
I might be telling you something you can't or aren't supposed to do though with a hotspot, you'd need a "prepaid gophone" plan//sim and to config that with your hotspot device.
I was going to do the same exact thing and do VOIP, but then figured why not buy a dirt cheap go phone with hotspot and pay the 60$.
Anyways, sorry I'm rambling. I'd say call ATT, see what they can do, but it might be a while on the phone, asking to be transferred to another, then another, then another person until you find someone that's been at it a while and knows just how to set it up.
You will find that people who work for ATT wireless, "some" of them, do not have a clue about what they are doing.
I've had them just keep saying, "OKAYYYY" to questions, and tech issues and they literally do not undertand me, then in the middle of my questions they say, "mmmm OKAYYY, happy you bye bye"....
So call ATT, if you must, get a 2 month package.