Hi, brand new user here!
I have a bunch of 3640's and 3620's. You can use the Wic 1t on the 2620. There are 2 slots for those.
For the 3640 you have quite a few options If you currently have a NM module (the large guys with the handles) those can take 2 Wic 1t's each.
Some above recommended the NM module with the token ring, that's fine but if you get the NM module with 2 fast Ethernet ports, that will work best for the long run if you are going for the CCNP or on to the CCIE. The reason I say that is if you want to match the CCIE topology, you will want the upgraded modules.
If you are just doing the CCNA and stopping there (why?) then the single ethernet (Keep in mind it's a 10mbps module) will be fine as it houses 2 wic 1t's.
Good luck in the pursuit!