Would this work for the internet on an amiga?

[amyren]

RJ45 != Ethernet

RJ45 is just the name of the plug, often used for ethernet. RJ45 plus is also commonly used for phone (ISDN) connections.

In this case its probably used an interface using CAT5 cables for nullmodem connections. (as already suggested kolla). Not sure if you need a crossover cat5 or a regular though.

[amyren]

There are a couple of threads on similar topic already on this forum that might be of interest.

Like this project (unfinished/abandoned?):
http://www.amiga.org/forums/showthread.php?t=51943&page=5

Or this product:
http://www.amiga.org/forums/showthread.php?t=49788

The last link was posted by myself a while back, regarding a specific product from connectone.
The product link in that old thread is not valid anymore, probably is the product discontinued. But they have similar products available on their website that I think could work on an amiga. Most interesting (due to price) is probably the one you find under evaluation board, Nano Socket Lan: http://www.connectone.com/?page_id=259
That board can be purchased from Mouser at $37

I was then browsing a bit at the Mouser online catalogue and find that they have other similar devices that looks to work the same way, like the WIZ110SR from Wiznet, at $26.87