Okay. I'm comfortable with prepaid service. I'm clueless on how to upgrade, and what would work with Net10, my current carrier. I have an antique LG bar-type phone, and it's two years old. I've been browsing unlocked phones, but Iphone seems to be the only game in town.
Basically, I'm lost. Some help here? 
The easiest thing you can probably do is just go by the store and talk to the salesperson. Tell them exactly what you want to do. They'll swap sims or program the phone for you. With prepaid services, you may have limited options and prices will be higher. Lower phone prices are the perks of regular service.
Www.mobilekarma.com is a trusted seller. Keep your choices to at least Good or Great. More info later when i am not writting from my phone.
Also www.cowboom.com for grade 6 or 5. 4 is too low.
Net10 uses the 850 and 1900 mhz GSM frequencies which are the same as an AT&T phones so you should be able buy a used one of them.
Amazon, Tigerdirect, and Newegg are decent sources. There's always ebay and craigslist too if you are looking for something used.
What type of phone are you looking for?
Well, I don't need a smartphone in general. I do need an upgrade from this LG phone which was new when texting was invented. I think.
What I listed above were retailers who could sell you a used or refurb'ed, unlocked handset.
This could also be as easy as just buying another handset directly from Net10. For simple and cheap, this could be a good fit at $29
http://www.net10wireless.com/#/phone-detail/samsung-t404g
Purchase online is an option but you can also buy a Net 10 handset in person at Target, Best Buy, Dollar General, WalMart and many many more retailers.
Once you have the new handset in your hands, you can pull the SIM card out of your old handset and put it into the new handset. Viola, you are making and sending calls from the new handset (all with the same phone number and no interruption in service.)
That's an idea. I'd have to order, unless someplace around here has one. Hm.
In reply to DoctorBlade:
Would you like a Samsung Rugby Smart i847 AT&T. It is Samsung refurbished still under warranty. For $150 shipped. Set to Net10 as it my DT phone 
haeheishman wrote: Cell phone jammer is an interesting and helpful device when we don’t want to be bothered by the cell phone noise. I just bought myself a cell phone jammer the other day, it is working great and BTW, it’s legal here in my country.
It's worth noting that it's illegal as all hell in the US and Canada, and you should consider whose important/emergency calls you may be blocking when you use one.
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