In the US, who needs to be registered as a MTB?

[mrtchipr]

I've been looking into the legality of using/accepting bitcoin in US and I'm seeing the term MTB come up a lot recently. Some say as long as you don't accept over $1,000 a day you're not classified under MTB and can trade bitcoin to USD freely.

I found a good explanation of what defines a "Money transmitting business"

provides check cashing, currency exchange, or money transmitting or remittance services, or issues or redeems money orders, travelers’ checks, and other similar instruments or any other person who engages as a business in the transmission of funds, including any person who engages as a business in an informal money transfer system or any network of people who engage as a business in facilitating the transfer of money domestically or internationally outside of the conventional financial institutions system - http://www.law.cornell.edu/uscode/text/31/5330

By looking at the definition above, I assumed that BitPay will be classified as a money transmitting business, because they will accept your BTC on behalf of businesses and convert it into USD for businesses to cash it, "outside of the conventional financial institutions sytem". However BitPay states in their blog that they believe they are not a MTB:

...The term “money transmitter” shall not include a person that only:...
(B) Acts as a payment processor to facilitate the purchase of, or payment of a bill for, a good or service through a clearance and settlement system by agreement with the creditor or seller; - http://blog.bitpay.com/2013/03/how-fincen-guidelines-affect-bitpay.html

So when it comes to accepting bitcoin as a payment, could we say that no one needs to register as a MTB unless you're an exchange like CoinBase, CampBX, MtGox, BitInstant, and etc?

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[BCB]

This regulation as it pertains to bitcoin in the us is VERY unclear and over broad.

Define "using/accepting bitcoin" as your use case will determine what regulation apply to you.

Money Transmission is regulated by the US Federal government as defined in the Bank Secrecy Act (BSA) and enforced by the Financial Crimes Enforcement Network (FinCEN).
There is no cost to register as a money service business.  You can do so on the Fincen.gov website.
This requires you to:
Keep records
File Reports to prevent
 - money laundering
 - tax evasion
 - criminal activities.
The BSA was amended by the USA PATRIOT act and that requires you to
 - Identify your customers

48 of the 50 States in the US require you to also get licensed as a "Money Transmitter."  This is to protect the consumers in each state. 
There are no money transmitter laws in:
Montana and South Carolina
New Mexico is also questionable (and there may be other)

I believe New York, Connecticut, Texas and California explicitly require anyone who serves clients in those states whether their company is foreign or domestic to be registered in those states.

In addition to the fees to apply in each state there are personal net worth requirements for each state. 
This starts at $1000 and goes up to $1M +
There is bonding required in each of these states of approximately the same range.
Each will do a criminal back ground check (some require finger printing)
They will evaluate you personal and professional finances
They will evaluate your business history.
Some require personal interviews with you and your key staff.

You may want to seek advice from an qualified lawyer familiar with US Money Transmission Law and Anti-Money Laundering(AML) and  Know Your Customer(KYC) requirements.

There is a very reputable attorney who post here regularly.  You may gain additional insight from this post.

https://bitcointalk.org/index.php?topic=206305.120

Good luck.