Digikey said EM7455_1104640 is a substitute. I just made a PCB for the EM7455_1103582. Are they pin-pin compatible? I cannot find any documents describing the differences.
Yes the modules from these two SKUs are pin-pin compatible so please rest assured. The major difference I can tell is 1104640 will be shipping with latest firmware TA’d for AT&T, Verizon and Sprint.
Yes, the SKU with this firmware is the only thing that is obsolete, the EM7455 is alive and well with no obsolete or EOL anywhere in sight.
If you want to continue using older firmware then you need to load it on your line, if you don’t have the files then search the source for something like 2.24 as older files are still there they just do not have direct links to them through the product pages. I have given an example below.
Then look under firmware and drivers for the relevant variant.