[severine]

Maybe this?

In addition to the expansion slot, the eMate also featured a single non-CardBus PCMCIA slot. It could be used for a number of different cards, including modems, ethernet cards, wireless cards, bluetooth cards, and flash memory (linear and ATA/Compact Flash).

Source: https://en.wikipedia.org/wiki/EMate_300

edit: OP answered!

[mattkevan]

Yes, with a compatible WiFi card you can get it on the internet. Simon Bell also maintains a Newton email client.