Complete Islands you get 100 credits for each island
Not any that are currently known (as of December, 2009, these are the only ways).
fb credits
Impossible
just use your phone whit out paying your own money
You can enter someone else's Multiverse room by invitation, at no cost to you. You can get multiverse with no credits if you are a Poptropica member. Paid monthly members can use anything in the store without spending credits. But they cannot keep the items used if they stop their membership.
The only way to get free Poptropica Credits is to complete islands (or the three games in the Store). You also get 25 credits for signing up. Otherwise, adults can purchase credits or memberships through the store.
You can earn 100 free credits for completing an island, but each island only once. You get 25 credits for signing up on Poptropica, and a possible 50 for registering your e-mail with the site. You can earn 50 credits for the free games Haunted House and Earth Day (in the Store), and for Dr. Hare's Secret Lab (which costs 250 credits to play, the main draw being the pink rabbot armor).
get it for your birthday, Christmas or Easter
That's the only two ways.
You can either ask someone to send you the product you want. Or you can earn credits or buy credits and then buy it. But other than asking someone to gift it to you, there's no other way to buy products without paying.
There are no credits in the clouds on Poptropica. This was someone's idea of a joke.
If you solve them you get 100 for every island. You can also finish the games in the store for more credits.