only gateway 3ds support play 3ds games on 3DS, and your 3DS must stay v4.1-v4.5, if your console updated to latest v6.3, gateway 3ds cannot work on it too.
r4i gold and other flashcart cannot play 3ds games on 3DS. they just support ds games.
currently only gateway3ds card can play 3ds games on your 3ds, but gateway 3ds currently can only work on V4.1-V4.5 system, can not work on 3ds latest firmweare, r4i gold or other r4 cards can not play 3ds games, only play ds games. the best r4i gold is this one http://www.dsflashcart.com/r4i-gold-3ds...-3ds-p-248.html
at present, only gateway3ds can support 3ds rom,yet,it has some requirment for N3DS Firmware version, so personally i recommend you buy r4i gold like this one : http://www.modchipfactory.com/wood-r4i-...s-lite-p-1.html , it uses famous wood firmware,with a good game compatibility to support almost all latest nds games.
For the time being,except gateway3ds, there havnt any card can support 3ds games. but GW3DS only work on N3DS V4.5 or lower version,so if your N3DS > 4.5, you cant use gateway 3ds . So, r4i gold is better for you,though it can just play nds games,yet,it was the most famous flashcart.
I have a regular ds lite with a dsone cart which i can play ds games fine but i was thinking on getting a nintendo 2DS since i dont care much about playing the 3ds games on 3d all i wanted is to play the 3ds games on 2d but i dont know which firmware this 2ds systems come with so i know if the gateway will work with it.
At present, the only flashcart which can play the 3ds games on 3ds consoles is Gateway 3DS, others can only play in DS mode, so if you want to play 3DS games on your 3DS console, try gateway 3ds.