Ting comes close
1) 6 dollars a month per activated SIM
2) only pay for what you use (more like pay for what category you fit this month)
3) BYO phone (buy a BLU, or a nexus, or anything really.) T-mobile compatible GSM and some CDMA.
4) No extra charge for tethering your tablet. it just uses your data.
Check out their rates. I am a happy customer.
I was paying AT&T $160 for 2 phones, now I pay Ting $45 to $60 for 3 phones.