in phone 3g is not working only 2g network is workiing

AT&T dropped 2g and 3g in favor of 4g and LTE.

It doesn't make sense to keep ancient bands.

Hello Kyan,

You are partially correct.

AT&T has discontinued their GPRS / EDGE 2G network.

The 3G networks launched by AT&T and other carriers were based on the UMTS standard, which was commonly called "3G" in marketing. This was improved upon with HSDPA, which got marketed as "3.5G." Then the super-improved HSPA+ was simply marketed to customers in Europe and Asia as "3.9G," briefly, before the whole world decided to market it as"4G." When your iPhone says "4G" in the top corner, it is still using (with many advances) the same network launched as "3G" a decade earlier. AT&T has not shut of its 3G networok, rather, it has upgraded it and now markets it as "4G." This means any "3G phone" is still compatible with AT&T's HSPA+ network. When an iPhone 3GS says "3G" in the top corner and an iPhone 4S says "4G" in the top corner, they could be connected to the same network.

LTE is the first true fourth-generation hardware. When your phone says "LTE" in the top corner, it is no longer using 3G.

Yes I know, its HSPA and HSDPA are commonly referred to as 4g, but in reality its 3.5G. But marketing wise they dropped 2G and 3G. GPRS is ancient and is not in the scope of OPs problem.