The specific recommendation for TracPhone was because they are not dependent on one network. TracPhone uses by agreement a whole host of vendors....so if one network is down or overwhelmed these phones will look for another option rather than just being dead.
There is no certainty with cell phones but this multiple network ability is a nice feature.
The description above applies to any cellular provider (although Tracfone doesn't actually 'provide' network access; I think of them more as a reseller of network access).
For example, say you have a tri-band cell phone (CDMA / TDMA / Analog) and subscribe to Verizon Wireless. If you are in a Verizon coverage area, your phone will likely use CDMA. If you are roaming, maybe your phone will have access to a CDMA or TDMA network that Verizon has a roaming agreement with; otherwise the much older analog system is hopefully available and Verizon has a roaming agreement; otherwise your cell phone is just a paper-weight.
Tracfone has roaming agreements with different carriers, and "re-sells" access using different technologies in different markets.
For example, I have a Tracfone and live in Ruidoso, New Mexico. Verizon has a CDMA network in this area. Guess what type of Tracfone's the local Wal-Mart carries? Yep, CDMA phones that use the local Verizon network. If I travel, I'll have access to any CDMA / TDMA / Analog network that Tracfone has a roaming agreement with (but this would also be true if I was a Verizon Wireless subscriber).
My sister lives in Albuquerque where both Verizon (CDMA) and Cingular (GSM) have good coverage. I just got her a Tracfone.
In Albuquerque, Tracfone has a business agreement with Cingular which uses GSM technology. Guess what type of Tracfone you can get at WalMart in Albuquerque? Yep, a GSM technology phone that uses the Cingular network within the Albuquerque area (and anywhere else that Tracfone has a roaming agreement).
I much prefer the coverage that Verizon Wireless provides in New Mexico. So instead of going with a GSM Tracfone from WalMart in Albuquerque, I instead bought my sister a CDMA Tracfone from the WalMart in Ruidoso and activated it with an Albuquerque zip code. So my sister ended up with a CDMA Tracfone with an Albuqueruqe phone number using the Verizon Wireless network. Of course, if she roams, she'll have access to CDMA or TDMA or Analog networks that Tracfone has roaming agreements with (but Verizon would provide a similar service). She won't, however, have access to any GSM network such as provided by Cingular -- her phone does not support GSM.
There is no such thing as a cell phone that supports both GSM and CDMA technologies. So you are stuck deciding between providers that use different technologies. My point is to pick the provider you think has the best coverage. But be aware that Tracfone, and other pre-paid plans, are doing the same thing and provide different options in different markets.
Hope this is a little clear,
Justin