Is "Spark" something that nCan be enabled with an Update ?
Can it be used on the previous generation 4G phones with an update ?
My theory is they will not update previous models so they can make New sales.
No, Spark uses different bands then reg LTE, so the phone's radio has to be capible of using those other bands.
The thing about the iPhone is that it is already compatible with those bands because it's pretty much a world every band phone.
LTE (4G)
700 Lower 700 (AT&T) / band 17 USA
750 Upper 700 (Verizon) / band 13 USA
850 Cellular / band 5 (V) Americas, Oceania, Brazil, Israel
850 Extended Cellular / band 26 USA
900 band 8 (VIII) Europe, Asia, Africa
1700 AWS / band 4 (IV) Americas
1800 DCS / band 3 (III) Europe, Asia, Africa
1900 PCS / band 2 (II) Americas
1900 PCS+G / band 25 USA
2100 IMT / band 1 (I) Europe, Asia, Africa, Oceania, Brazil, India, Israel
WCDMA (3G / 4G)
850 Cellular / band 5 (V) Americas, Oceania, Brazil, Israel
900 band 8 (VIII) Europe, Asia, Africa
1700 AWS / band 4 (IV) Americas
1900 PCS / band 2 (II) Americas
2100 IMT / band 1 (I) Europe, Asia, Africa, Oceania, Brazil, India, Israel
CDMA (2G / 3G)
800 ESMR / BC10 Americas
850 Cellular / BC0 Americas, Oceania, Brazil, Israel
1700 AWS / BC15 Americas
1900 PCS / BC1 Americas
GSM (2G)
850 Cellular Americas, Oceania, Brazil, Israel
900 Europe, Asia, Africa
1800 DCS Europe, Asia, Africa
1900 PCS Americas
plus LTE bands 19, 20 / not all versions support CDMA / LTE 850 (band 26) on Sprint version only