Look for it in google in order to find the celebi event

When you knock out a roaming Pokemon, it will faint and then start roaming again, but with its health at full.

You are roaming only when you are out of your calling area. If you live in CA and call Maryland from within your calling area, it's not roaming. However, if you live in Maryland and calling from CA, you are roaming.

No, satellite phones do not usually have attached roaming charges. Very few cell phones have roaming charges these days, and so roaming isn't something that needs to be worried about.

T-Mobile does not charge a seperate fee for roaming under their unlimited plans. Roaming charges are starting to be phased out.