This kind of thing happens, for sure. Many operators place a default APN on the SIM card or in the USB modem itself (only on operator-branded versions). Mind you, it’s not on ALL operator-sold modems, which is why the APN field is in the UMR, like in all 3G routers. I think it’s great to avoid the use of an APN, but considering you don’t know which one it is you’re using, you can always specify it in the UMR, and it’ll use that one instead. The UMR will always check if there is an APN in the modem first if the setup does not include a filled APN field.

For those of you using CDMA, there is no need for an APN at all since it’s a different setup altogether. It usually requires a username and password, otherwise many operators run the default “cdma/cdma” as user/pass.