I know that this has been addressed to, but since it's Pokemon-related, I can't help but giving a bit more of an in-depth response of my own two cents.
The Pokewalker looks like a Tamagotchi? This is pretty much the only point I can understand. They both have three circular buttons below the main screen that's monochromatic and has a creature on it.
Acts like a Tamagotchi? I've been a passive Tama fan for a few years and I've been using my Pokewalker occasionally since I got it on launch in the US in March. I can't see the similarities at all. The Tamagotchi is a stand alone device, for the most part. You get your egg on it, hatch it, and you can raise it over again all by itself. Throughout the life cycle, you can get some of ~50-ish Tamas. The Pokewalker is a device that requires HGSS. Without one of the games, you might as well throw the Pokewalker out or sell it. Using HGSS, you can transfer one of 493 different creatures. You don't take care of it, it's perfectly fine without you. Just walk around and level it up a bit so it's better in battle when you transfer it back. You can also collect some items and new Pokemon to return to your game.
The purpose of the Pokewalker, at least as I see it, was to help complete your Pokedex. Starting with the third generation, due to more and more Pokemon being introduced, old ones can easily get left behind. When the fourth generation started in 2007 (US launch,) it was possible to get all 493. (Well, 490, if you're not counting the yet-to-be-revealed event Pokemon Darkrai, Shaymin, and Arceus.) This was fairly straight forward at the time, since most Pokemon fans already owned some of the third generation games, Ruby, Sapphire, Emerald, Fire Red, and Leaf Green. As the fourth generation continued with Platinum's launch in 2009, less and less people owned the third generation required to complete the Pokedex as more fans entered the franchise. (It didn't help Ruby and Sapphire were the lowest selling main games in the franchise. Which is a shame, since they're my favorites.) They tried to fix this by adding a few more Pokemon in Platinum that were impossible to get, but it didn't help much. To further complicate things, the DSi removed the GBA slot, which completely cut off access to the third generation. If you didn't know someone that had the Pokemon you needed, you had no chance. With HGSS being the last entries in the fourth generation, they released the Pokewalker to help catch up a few missing species with people's Pokedexes before the fifth generation with Black and White started. (And to remake Pokemon Pikachu 2, see point about infa-red below.) With a few Pokemon being exclusive to HGSS without trading or migrating using the Pokewalker, this filled the gaps for a few people. Even with the other three regions being featured in the fourth generation, Sinnoh (Diamond, Pearl, and Platinum,) Kanto, and Johto (Heart Gold and Soul Silver,) Hoenn Pokemon had a bit of a chance to catch up. ... If you're not a Pokemon fan, I doubt you understood most of that. Tl;dr- The Pokewalker was made more of a way to get Pokemon and not as a virtual pet.
Infa-Red communication. It's true that both Tamagotchis and Pokewalkers can connect with each other via infa-red and give each other gifts, but that's as far as infa-red goes. With Tamagotchis, you can build up friendships, visit each other, and play games. You can even marry other Tamas once you build up a high enough relationship. With the Pokewalkers, the infa-red port was pretty much needed in order to connect with HGSS in the first place, which is the port's main purpose. However, in the original Gold and Silver, there was a house in Viridian City called the Trainer House. Every day you could battle a trainer, and it would be a CPU controlled team of the person you last used Mystery Gift with using the Gameboy Color's infa-red port. In HGSS, you can now fight multiple people (up to ten I believe, but still one battle per opponent per day,) which is determined by people you connected Pokewalkers with.
Not to mention, Pokemon actually had the infa-red ports first. The Pokemon Pikachu 2 (also known as the Pocket Pikachu 2) came out in 1999 and featured an infa-red port that let you connect to your Gameboy Color using Gold and Silver to send items back to the games using Mystery Gift. (Judging from the commercial, you could also connect to other Pokemon Pikachu 2... Not exactly sure how this works though, since I never owned one.) In 2001, another monochromatic device with an infa-red port called the Pokemon Mini came out. This was like a mini Gameboy in the fashion that it had multiple carts that you can put in and take out of it. It had an infa-red port that allowed you to connect to others and play mini games on it. One of the games for it was a virtual pet in which you take care of the Hoenn starters, but since it was Japanese-only, released near the end of its lifespan, and the details are so scarce on it, I have no idea if the virtual pet game in particular took advantage of the infa-red port... And now, on the other hand, the Tamagotchi Connection V1 came out in 2004, 5 years after the Pokemon Pikachu 2.
Tl;dr- I don't get how in any way the Pokewalker is a copy/ripoff of Tamagotchis.
Also, I don't think you could sue anyone if you don't own the rights to Tamagotchis in the first place.
Yes, I usually end up typing paragraphs when I respond to something Pokemon-related like this.
The pokewalker is nothing like a tamagotchi.
