Good comparison of prepaid plans:

http://www.prepaidphonenews.com/2011...and-plans.html

AT&T GSM 850/1900, LTE Data
LTE Bands: 2, 4, 17

Basic and Messaging Phones (No Smartphones, iPhones, etc.)
No monthly fee - 10¢/minute, 20¢/text, Data 1¢/5KB of use
$2/Day (Only billed fee on days used) - Unlimited Domestic Talk and Text, Data 1¢/5KB when Used or $1/Day for 100MB

Smartphone or Basic/Feature Phones
$30/month Unlimited Domestic Talk and Text; Data is not included: 1¢/5KB of use, or $5/Month 100 MB
$45/month Unlimited Domestic Talk and Text, 1.5GB Data at "3G" speeds, thereafter throttled to 128Kbps
$55/Month Unlimited Domestic Talk and Text, Includes Unlimited calls to Mexico; 1¢ per minute for calls to Canada, calls within Mexico and Canada, and from Mexico and Canada to select countries, plus unlimited messaging while roaming in Mexico and Canada. 1 GB Data at "3G" speeds, throttled to 128 Kbps thereafter
$60/Month Unlimited Domestic Talk and Text, Includes Unlimited calls to Mexico, Unlimited Texting when in Canada or Mexico, 4 GB Data at "3G" speeds, throttled to 128 Kbps thereafter

Verizon CDMA, LTE Data
LTE Bands: 2, 4, 13

Pay-as-you-go (Feature/Basic Phones Only)
Daily access fees are billed only when device is used
$1.99/Day - Unlimited Domestic Airtime, Text Messages are 2¢/message (in or out), Picture Messages are 25¢/message (in or out), Mobile Web access 99¢/24 hour period
99¢/Day Unlimited Verizon to Verizon Calls, Standard Airtime Calls 25¢/Minute, Text Messages 10¢/Message (In or Out), Picture Messages 25¢/Message (In or Out); Mobile Web Access 99¢/24 Hour Period
$0.00/Day - Standard Airtime Calls 25¢/Minute, Text Messages 20¢/Message (in or out), Picture Messages 25¢/Message (in or out), Mobile Web access 99¢/24 hour period

Can add the following monthly text messaging options:
$20/month for Unlimited Messaging to anyone on any network in the U.S.
$10/month for Unlimited Mobile to Mobile Messaging with Verizon Wireless customers PLUS 250 additional messages*

Feature Phone Monthly Plans
$35/Month 500 Standard Airtime Minutes, Unlimited Domestic Texts, Unlimited Texts to Canada, Mexico and Puerto Rico, 500MB Mobile Web
$45/Month Unlimited Standard Airtime Minutes, Unlimited Domestic Texts, Unlimited Texts to Canada, Mexico and Puerto Rico, 500MB Mobile Web


Smartphone
$45/month Unlimited Domestic Talk and Text Includes 1GB LTE Data, 500MB included when signed up for monthly autopay. Data Stops once allotment is exhausted.

Additional Data for Monthly Smart or Basic Phone Plans
$5 for 500MB, $10 for 1GB or $20 for 3GB. Data access stops once data allotment is exhausted, would need to purchase additional data for the month or restart bill cycle for a new 30 Days

T-Mobile GSM 1900, LTE Data
LTE Bands: 2, 4, 12

$3/month 30 minutes of Airtime or 30 Texts (or a combination)
Data can be added: $5/day 500MB High Speed Data (LTE) or $10/week 1GB High Speed Data (LTE)

$30/month 100 Minutes Airtime, Unlimited Text, 5GB of High Speed data (LTE, HSDPA+) then throttled to "2G" speeds. Includes International texting at no charge to select countries Must be activated on-line, or purchased from Wal-Mart
$35/month Unlimited Airtime, Unlimited Text, No Data Included

The following plans include Unlimited Airtime, and Unlimited Text, Speed is throttled to 8 Mb/s regardless if a higher link is available, once data allotment is consumed throttled to "2G" speeds, or a max of 128 Kb/s. Price is listed monthly.
$40 - 1 GB Data
$50 - 3 GB Data
$60 - 5 GB Data

Add Unlimited landline, and texting to select countries for $10/month, Calls to mobile carriers in select countries are 20¢ per minute
Add Unlimited landline, mobile calling and texting to select countries for $15 per month

If the device supports it, these plans also have T-Mobile WiFi calling available at no charge.

Sprint CDMA, LTE Data
No longer offers branded pre paid services, all plans are sold through Boost subsidary

H2O

U.S. Cellular CDMA, LTE Data
LTE Bands: 5, 12

Plans are listed per month
"Ready Connect" (Available at Wal-Mart and Amazon.com, and other stores)
$35 - Basic Phone Only - Unlimited Talk, Unlimited Text, Unlimited Mobile Web
$45 - Smartphone - Unlimited Talk, Unlimited Text, 1GB Data
$55 - Smartphone - Unlimited Talk, Unlimited Text, 2GB Data
Maximum of 200MB can be used off network.
Data stops when allotment is exhausted, additional buckets can be purchased for $5/250MB, $15/1GB, $25/2GB

"Simple Connect" Plans all include Unlimited Talk, Text, and Data, the high speed allotment varies depending on the plan, prices are monthly
$40 - Basic Phones Unlimited Data
$45 - 1GB Data
$55 - 2GB Data
$65 - 4GB Data
Data is throttled to "1x" speeds thereafter (max of 196 Kb/s)

TracFone GSM 850/1900 or CDMA
Annual Cards (Good for 365 Days from Activation)
$199.99 1500 Minutes
$159.99 1000 Minutes
$119.99 800 Minutes (Plus double minutes on future refills)
$99.99 400 Minutes
$19.99 Package adds double airtime to all future refills

Pay-As-You-Go
$79.99 450 Minutes for 90 Days
$39.99 200 Minutes for 90 Days
$19.99 60 Minutes for 90 Days
$9.99 30 Minutes for 30 Days (online only)

Web Access for Android Phones
$50/2GB
$20/750MB
$10/300MB

Red Pocket (Link)
512MB - $5
1GB - $10
3GB - $30
5GB - $50
Uses T-Mobile's 4G/LTE network
All plans except 512MB are throttled after exceeding data usage.
SIM cards can be purchased inexpensively through Amazon and ebay

Cricket Wireless GSM 850/1900, LTE Data
AT&T Wireless Subsidy
Plans are monthly, and include Unlimited Talk and Texting, Included data varies; LTE speeds are throttled to 8Mb/s, HSDPA+ is throttled to 4Mb/s, $5 discount available when on autopay
$25 - NO Data Access
$40 - 2.5GB
$50 - 5GB Adds Unlimited Calling and Texting to Mexico, plus 35 additional countries
$60 - 10GB Adds Unlimited Calling and Texting to Mexico, plus 35 additional countries
$60 - 20 GB (Promotional Plan) Adds Unlimited Calling and Texting to Mexico, plus 35 additional countries

MetroPCS GSM 1900, LTE Data
T-Mobile Subsidy
Plans are monthly and include Unlimited Talk and Text. Included Data Varies, once package data is exceeded speed is throttled to "2G" speeds (128Kb/s max), prices include add fees and taxes

$40 - 2GB Data (promotional)
$50 - 4GB Data (promotional)
$60 - Unlimited Data

$50 Unlimited Data plan is available when purchasing a device from MetroPCS, BYOD is not available on that plan

Add-ons
$10/month Mexico Calling: Unlimited Calling to Landlines, 1000 minutes to mobile phones, Unlimited texting to mobile phones, 200 minutes and 200 texts when traveling in Mexico
$10/month World Calling - Select countries include unlimited calls to landlines, Unlimited texting, 200 minutes to mobile phones; 200 voice roaming voice minutes, Send 200 text messages, unlimited incoming text messages

Net10 GSM 850/1900, LTE Data
Pay as you go
$100 - 1500 Minutes, 180 Days
$60 - 900 Minutes, 90 Days
$45 - 600 Minutes, 60 Days
$30 - 300 Minutes, 60 Days
$20 - 200 Minutes, 30 Days

Monthly No Data Plans (Good for 30 Days)
$25 - 1000 Minutes
$30 - 500 Minutes
$15 - 200 Minutes

Monthly Unlimited Plans - Price is monthly. Includes unlimited Talk and Text, Amount of high speed data varies per plan and is then throttled to 64 kbps thereafter
$35 - No Data
$40 - 500 MB (additional 250 MB with autopay)
$50 - 3GB
$60 - 3.5GB (additional 1GB with autopay)
$75 - 5GB (additional 1GB with autopay)

Virgin Mobile CDMA
Sprint Subsidy

Monthly Basic Phone Plans "PayLo", Text Messages are 25
$40 Unlimited Talk, Unlimited Text, 50MB of Data
$30 1500 Minutes of Talk, 1500 Text (in and out), 30MB data
$20 400 Minutes, 15¢ per text, 25¢ per picture message, $1.50/MB for Data

Unlimited Plans
$20 300 Minutes and Text
$35 Unlimited Talk and Text, 250 MB 3G/4G data throttled thereafter
$35 Unlimited Text, 300 Minutes 2.5GB 3G/4G data, throttled thereafter
$45 Unlimited Talk and Text, Unlimited International Text, 100 International Voice minutes, 1 GB 3G/4G data throttled thereafter,
$55 Unlimited Talk and Text, Unlimited International Text, 100 International Voice minutes, 3 GB 3G/4G data throttled thereafter

Data Share Plans
Plans are monthly and include Unlimited Text, Voice minutes vary by plan, data allotment is 2.5 GB of 3G/4G data and is throttled after the included data is exhausted, $20 starter kit is required and available only at Wal-Mart
$35 - 300 Minutes
$45 - Unlimited Talk

Additional data
$10/Month - 1 GB
$15/Month - 2 GB
$25/Month - 4 GB
$35/Month - 6 GB
$65/Month - 12 GB
$85/Month - 20 GB

$2 One time 100MB DATA
$5 One time 500MB DATA

$5 VOICE EXTENDED COVERAGE 60 MINUTES (ROAMING)
$2.50 DATA EXTENDED COVERAGE 10MB (ROAMING)
$5 DATA EXTENDED COVERAGE 20MB (ROAMING)
$10 DATA EXTENDED COVERAGE 40MB (ROAMING)
$2 100 MINUTES OF TALK (Good for 30 Days)
$5 300 MINUTES OF TALK (Good for 30 Days)

Ultra Mobile GSM 850/1900 UMTS 1700/1900 LTE 1700
LTE Bands 2, 4, 12

Roams off T-Mobile with theoretical full access to the T-Mobile network, but network coverage is slightly reduced as is 4GLTE coverage

All plans include:
Unlimited domestic calling
Unlimited domestic SMS/MMS
Unlimited global SMS/MMS
Standard features: 3-way calling, caller ID, voicemail, 411

Plans range from $19-49/month and generally include free international calling (landline/cell) and local access numbers for friends/family to call.

SIM card costs $1. See Ultra.me for more info.

You can purchase SIM and plan through 3rd parties such as EZKonnect or even Amazon for a discount.