Both on Android and iOS, the phone can be your hotspot, sharing the Internet using BT or WiFi.
Why would you want an extra LTE box ? To carry more cr*p around ?
If you put in a data-only SIM, if that is your plan, you can do that.
Here in Denmark, plans with 5 hours talk + 8 GB monthly data is around $15/mo, $3 extra for LTE, which brings the speed up to 65/25 Mbit/s typical. Unlimited talk + 100GB/mo data is $43/mo, or $35 for data only SIM. So not really worth it to drop the voice and SMS texting part yet. Remember you will los SMS texting if you drop voice plans. Then it will be iMessage or whatever you use only.