Are APNs like a vpn for mobile devices to access the public internet? Based on the experience that I used Mobile roaming outside my country. The provider would connect back to the original country via local providers.

• Breakout to the Internet using the local roaming partner, or

• Tunnel to the home network via the local roaming partner, and breakout to the Internet there.
  

Both models are viable particularly if the roaming partner and home network are basing their roaming architecture on IPX rather than GRX.

Local breakout improves performance because it is low-latency, while remote breakout is often preferred because it does not complicate billing and other traffic controls imposed by the home network. 

My anecdotal experience has been that you will have local breakout sometimes, and remote breakout most of the time. This will also vary from provider to provider. I also find that home networks tend to prefer remote breakout, while users, unsurprisingly, will have a better experience with local breakout.

I've never been able to find conclusive data on which mobile operators implement local vs. remote breakout. It doesn't appear that the GSMA mandate any one model over another against their membership, so mobile operators are likely making individual choices on what they do.

Either way, with an IPX-based roaming architecture, it is really just a glorified l3vpn cloud built on a standard IP/MPLS network.

If you have time, the below is an interesting read:

    https://www.gsma.com/newsroom/wp-content/uploads//IR.34-v17.0.pdf

Mark.