Want to save money on your phone bill? How about switching to an MVNO?

I have never understood why (contract free) people pay 100s of dollars on their phone bills being on of the Big 4 cellular networks in the US, namely: AT&T, T-Mobile, Verizon and Sprint. Talking to some of those people, I realize they don't even know they have an option, namely an MVNO. MVNO stands for Mobile Virtual Network Operator. These are carriers who supply their own plans to customers but use one (or more) of the Big 4 networks I listed. In other words, you do stand to save money on your monthly bill and that too, without losing the network you love!
Sounds too good to be true, so what is the catch? Well, the catch is that customers using one of these MVNO plans may be deprioritized by the Big 4 in moments of network congestion or their data may be throttled when they reach a specific threshold in comparison to customers who are directly using the Big 4. But, for all practical purposes, you won't feel a difference. I can say that having tried almost 10 of those myself.
In case you are on board with the idea and would like to reduce your monthly bill to something under $40 for an individual line, I have listed some major MVNOs and their plans below.
How do you start? Well, first you need to know which Big 4 network works best for you (has the strongest coverage in your home & work area). You can either talk to your colleagues/friends to find that out OR use one of the best sites for the purpose: OpenSignal. They have an app as well - try it out once if you haven't already!
Once you are locked in on one of the Big 4s, use the table below to figure out which plan works best for you. All plans listed below are BYOP cheapest individual plans under $40, no contract, with unlimited talk and text within US and with at least 1 GB of 4G LTE data as of today 8/3/2019.
International calling, if not included already, can be added additionally in all of the plans.
In case Visual Voicemail is not available, you could use YouMail as an alternative.
'Unlimited Music' mentioned below means those providers allow you to stream unlimited music (using apps like Spotify) without counting it against your data limit.
The 'Port Out Information' in the table below is sourced from: http://www.prepaidphonenews.com/2014/02/porting-your-number-how-to-find-your.html
I have arranged the MVNOs below first on Big 4s, then on lowest plan price, then on most data and then finally on other features. You can visit each of these on their websites in case you'd like some of their other plans:

MVNO	Network Used	Plan	LTE Data	Visual Voicemail	International Talk	Unlimited music	Taxes included	Auto recharge discount	Multi line/family discount	Port Out Information (in case you'd like to switch out of this MVNO)
H2O Wireless	AT&T	$30	3 GB	No	Yes	No	Yes	Yes (10%)	Yes	You need to call customer service at 1-800-643-4926 and ask them to release your number for porting and tell you your account # and PIN. They will ask you to provide the 3 most recent outgoing calls to verify that it's your number. Account# is 8 digit while the PIN is 4 digit.
Cricket Wireless	AT&T	$30	2 GB	Yes	No	No	Yes	Yes ($5, not on $30 plan)	Yes	Account number can be found online or by calling the Cricket Porting Department at 1-866-351-7678 (then option #2). The passcode is the four digit Authorization ID (or "AID") that you set up when you activated when setting up your onlie account and which you need to enter when making changes to your account online.
Airvoice Wireless	AT&T	$20	1 GB	No	Yes	No	Yes	No	No	Account # is the SIM Card number and password is last 4 digits of phone number.
Black Wireless	AT&T	$25	1 GB	No	Yes	No	Yes	No	No	You need to call customer service at 1-800-643-4926 and ask them to release your number for porting and tell you your account # and PIN. They will ask you to provide the 3 most recent outgoing calls to verify that it's your number.
Red Pocket	AT&T/T-Mobile/Verizon/Sprint	$19	1 GB	No	Yes	No	No	Yes ($5)	No	Account# is your phone number and PIN is the last 4 digits of your sim card number (ICCID).
Net10 Wireless	AT&T/T-Mobile/Verizon/Sprint	$20	1 GB	No	No	No	Yes	Yes	No	Account # is NOT the Phone Number – It is the MEID or IMEI serial number of the phone (this can be found on the back of the phone itself - under the battery, so remove the battery!) Or, if your are using a BYOP SIM Card, it will be the last 15 digits of your SIM Card number. NET10 doesn't use passcodes, use 0000 if the operator you are porting to requires a passcode.
Virgin Mobile	Sprint	$35	5 GB	Yes	No	Yes	Yes	No	No	You need to contact Virgin Mobile customer service to get your account number - it will be a 9-Digit number - and the passcode is usually the customer's birthday in 6-digit format (2-digit month/2-digit day/2-digit year...example: 011065 for January 10th 1965) UNLESS you changed it to something else.
Boost Mobile	Sprint	$35	3 GB	Yes	No	Yes	Yes	Yes ($5)	Yes	Call Boost at 1-888-266-7848 to get your 9-digit account number. Ask the account representative to give your the account number "for your personal record". Your passcode is your 4-digit PIN with Boost, the same PIN that you login with.
Lycamobile	T-Mobile	$19	1 GB	No	Yes	No	Yes	No	No	You need to call CS at 1-866-277-3221 to get your account # and password.
Ultra Mobile	T-Mobile	$19	1 GB	No	Yes	No	Yes	No	No	Dial 611 and press 5 to see your account number. Or call Ultra customer service at 888-777-0446 to get your account number. The passcode is the last four digits of your Ultra Mobile phone number.
Metro	T-Mobile	$30	2 GB	Yes	No	Yes ($40 & up plans)	Yes	No	Yes	Account number: 9 digit number, check on billing statement, Password: 8 digit code you use when verifying customer service
Simple Mobile	T-Mobile	$25	3 GB	Yes	Yes	No	No	Yes	No	Account number is the last 15 digits of the SIM ID and the passcode is the last 4 digits of the SIM ID.
Total Wireless	Verizon	$35	5 GB	Yes	No	No	No	Yes (5%)	Yes	Account # is the phone's MEID. There's no passcode, use 0000 if the operator you are porting to requires a passcode.
Page Plus Cellular	Verizon	$30	3 GB	No	Yes	No	Yes	Yes	No	Account # is the 10 digit phone number. Passcode is always the last 4 digits of the phone number, unless you have changed it.

Once you have picked an MVNO plan, order a sim and transfer your number to them. Here is the port out information of each of those Big 4s:

AT&T (postpaid) - Account number will be on the bill (it is NOT the phone number) - password will be your online password. For bundled bills, the account number will be a 12-digit number under your wireless account summary. Also, (only for bundled bills) you will need to call AT&T customer service for the passcode - it will be a 4 digit PIN number that they provide to you.

T-Mobile (postpaid) - 9 digit account number (NOT phone #) on your bill and can be a word for the password.

Verizon (postpaid) - Account # (on bill) ends in -00001 - passcode is "call-in" passcode when you call customer service. It is usually the last 4 digits of your social security number (unless you specifically changed it to something else).

Sprint (postpaid) - Account # is NOT phone number, it's is a 9-digit number which can be found at the top center of your bill and on your online account page. Your passcode is your "call-in" passcode when you call customer service. You can set up or change your PIN on your online account page.