Amaze supports these radio modes:
WCDMA / HSPA+ 42 (3G / 4G)
850 Cellular / band 5 (V) Americas, Oceania, Brazil, Israel
1700 AWS / band 4 (IV) Americas
1900 PCS / band 2 (II) Americas
2100 IMT / band 1 (I) Europe, Asia, Africa, Oceania, Brazil, India, Israel
850 Cellular Americas, Oceania, Brazil, Israel
900 Europe, Asia, Africa
1800 DCS Europe, Asia, Africa
1900 PCS Americas
It also supports data at these speeds:
HSDPA, 42 Mbps; HSUPA
Here's my understanding--the Amaze is technically not a 4G handset, as it supports only up to HSPA+, which is not by the standards considered 4G, but only an improvement on 3G. However, 42Mbps is a huge improvement on 3G thus giving the speed one might expect someday on a 4G network, but not providing a true upgrade path towards the standards imposed on a 4G network.
In simplest terms, the Amaze has a very fast radio, but is not technically 4G.
To complicate things, the standards have been changed to call T-Mobile's HSPA+ network a 4G network:
This doesn't yet answer your question.
In my understanding, there was no crippled version of the Amaze 4G marketed, such that ALL Amazes had ALL radio frequencies available.
So then, if your provider sends data over any of the aforementioned frequencies, you can receive it, at the speeds at which they send it providing suitable reception, and not any faster than 42Mbps.
Here is a list of HSPA+ networks:
Someone else here can tell you if you should update your radio firmware or not.