[Question] Umi emax straight talk APN settings

[epatnoe]

I just got an ATT sim from straight talk and after activation still no mobile networks available. I have put in new APN settings: from straight talk...
NAME: STRAIGHT_TALK
APN: RESELLER
MMS_APN: default,mms,supl
MMSC: [Only registered and activated users can see links Click here to register]
MMS PROXY: proxy.mobile.att.net
MMS PORT: 80, please note that these values are case sensitive.

Still no mobile network. Any help would be appreciated.

[Sniper47]

Umi eMax [stupidly] does not support 850 GSM or 850 WCDMA frequencies. Much of AT&T is still on 850 for GSM/WCDMA. Try T-Mobile MVNO.

[epatnoe]

Thank you. I'll try T-Mobile. I'll be back if there are issues. Glad I found you guys.

[Sniper47]

No problem. Maybe borrow a friend's SIM or order through eBay MVNO SIM for $1. Let us know how it turns out.

[epatnoe]

Thank you. i'll try T-mobile

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Forgive my ignorance, how does a Mvno sim work? There are a million on eBay, how would I know which could work? Will they list my phone as one that's compatible? Sorry for the lack of knowledge.
-Eric the old guy