Refarm and 4G LTE - what are the final frequencies

Have a couple of questions regarding TM's 4G LTE frequencies.

TM 4G LTE uses AWS 1700 and 2100MHz right now.  Is a phone required to support BOTH 1700 and 2100MHz to work w/ 4G LTE?

Also, I am reading this article and I wonder if this is true:

"Once these network upgrades are completed in 2015, T-Mobile will offer LTE in the 700MHz, 1700MHz, and 1900MHz bands."

If so, this means one year later a phone that needs to work with TM 4G LTE would requires all these bands?

So any phone that supports WCDMA AWS 1700/2100MHz only now would be totally useless a year later?

Thx.