Does an iPhone 3G (in excellent working and cosmetic condition) have any collectible value? If not, do you think it would in the future (if it stayed in the same condition)?

I wouldn’t. Sure, there is an off chance that someone might find this to be an interesting curiosity in 10 years. But technology-wise, it is already out of date and will continue to get even more out of date. So even if the look/feel is a museum piece, it will never work as an effective phone in the future.

Keep in mind that the battery will deteriorate over time as well. At some point, no matter how much care you take, it won’t take a charge any more. So you won’t be able to power it up anyway, after a while.

Summary: not worth it as a collectible.

It will not make you rich. But no harm in holding onto it. I have a snow g3 imac on my dining room table. Still works running OS 9. Cool conversation piece.

But on your phone I would really suggest yanking the battery. It will leak if it hasn’t already.