Why does my data connection work WITHOUT an APN?

[mprowe]

I have recently joined SMARTY. Soon after activating, I got (what I suspect is a generic) message advising me to update my APN if I was interested in roaming. I am, so I did.

However, due to finger trouble, I entered "mob.asn.net" (note the N in ASN) and not "mob.asm.net". Surprisingly (to me) this worked. Intrigued, I started experimenting and all the variants that I tried (including a null entry) worked.

Why/how is this?

Regards, M.

[MSF]

@mprowe If you are not actually roaming, then I do not think that it affected anything.

My limited understanding is that it comes into play when you are registering with a foreign network.

[WelshPaul]

APN only matters when outside the UK. You can put Mickey Mouse in the APN field and data will work just fine. 

[mprowe]

What is the position in reverse?

If I have a French SIM (Free) in my router, will Three complain because the APN info is wrong?