EXCLUSIVE

"The Real Housewives of Atlanta" star Apollo Nida is learning who his real friends are while he's in prison, and two very unlikely suspects have remained loyal ... Kandi Burruss and Todd Tucker.

Apollo phoned us from prison to say most people won't take his call, so he was really surprised when Kandi and Todd took the time to jawbone with him when he reached out.

What's more ... Apollo says the couple constantly check up on him and even put money in his commissary account.