Correction: Boost and Cricket both use the Sprint CDMA network.
If he's bringing his own phone from a different country he'll need a GSM/HSPDA network. Globally, LTE should be the single standard once 4G is on worldwide rollout, but it won't be there for years. Maximum interoperability requires GSM. I've spent way too long looking at mobile phone standards in the last couple of weeks.
Go to the T-Mobile web-store and buy a SIM activation kit for $1. When you receive it, follow the activation instructions on the web and when it asks you to choose your plan, select "Monthly 4G $30"
* Unlimited internet*
* Unlimited Text
* 100 minutes talktime
It's basically a prepay deal where the available balance will drop by $30 a month, so you just need to top-up once a month, and make sure you have enough credit to cover any calls you make over the 100 minutes No ongoing contracts.
Deal is web-only.
*Unlimited internet means up to 5GB at HSPDA+ speeds.