Is it correct that when using the Moto G with VoIP there would be much less radiation?
Eh. Not really. As our friendly but necrotic 21st president has pointed out above, the scientific studies have been inconclusive regarding cancer. That said (and before I get any further) it is worth note to point out that although the radiation from phones is non-ionizing,
it does still cause surrounding tissues to warm up around 1°C or more due to prolonged exposure, which can potentially cause its own host of issues on the cellular level. I might also point out that WiFi data radiation for VoIP services can be just as heavy and ongoing as 2G/3G voice, if not more so. Data services on handsets (both mobile and WiFi) are likely to cap out at the handset's SAR rating to reduce potential data loss because the handset is not expected to be against the body, whereas actual GSM or CDMA voice services tends to use the lowest signal strength that can be utilized to maintain the signal based on tower proximity and reception.
However, I can think of far greater reasons
not to go with Republic than any sort of concern over radiation exposure. The draconian legal contract you sign up for and have to agree to, the quality of the service, the price not being as competitive as it appears against the competition (especially with data packages)... these are all points that I've gone over ad nauseum around these forums for years, and I know of several former Republic users here who would agree on the points presented. It's simply not worth the money and the hassle when you know there's better for nearly equal or less.
If you're looking and open to the possibility of switching carriers and you're picking the Lumia for reasons other than just price alone (as in, you'd prefer the handset specifically over an Android device), it's worth noting that
you would be eligible to unlock the handset to take to any GSM MVNO after only four additional months on T-Mobile. From that point you could potentially go to P'tel or Airvoice, or any other T-Mobile or AT&T based provider that
might provide cheaper services for what you actually need than what your current package does. It's worth doing the math. If you don't actually need a smartphone or mobile data access, that could also help save a lot more money.
If it is about the money,
Prepaid Phone News runs a weekly "On Sale This Week" post every weekend.
Here's their current one for this week. Note that the T-Mobile Lumia 521 is on special for $49.88 at Walmart and Groupon has a refurbished and
already carrier unlocked HTC MyTouch 4G Slide for $67.99 (it's an older build of stock Android 2.3, but
well supported by CyanogenMod 9 which is equivalent to Android 4.0 if you or a family member are technically inclined), amongst other such deals. Of course, feature phones are even cheaper and there's also Ebay and Craigslist
if you know how to look for a good used handset and
know what you want.