Is there any way to switch a land line number to a cell phone?

if you are in US maybe you can use service from company like http://phone.com

You can't add it to your cell phone, unless your phone and carrier multiple numbers.  That is very rare in the United States. You replace your existing cell phone number with your landline number. That is probably not what you want, since you probably like your cell phone number,. While you can move a landline to a cellphone or a dedicated VoIP service, you can NOT move it directly to Google Voice. To move a number to Google Voice, it needs to move FROM a cell phone. So,to get a Landline to Google Voice is a two step process - move to a cell (mobile) phone, then to Google Voice.  You can get a cheap, disposable prepaid phone to execute the first step of process. See: https://support.google.com/voice/answer/1065667?hl=en

If 212 means Manhattan (but really for anywhere in the U.S.) the feature you're looking for is called Local Number Portability.When you get a 'new' phone service, the service provider may (with a fee) offer to port your old phone number to the new service. In practice, this means whenever someone calls your old land-line home phone in Area Code 212 your new phone rings, and your land-line is cancelled.You can get a Google Voice account (or other similar service) and have your number ported to it, then have Google Voice re-direct the call to an existing cell phone number.

Yes this will not be a problem with any of the major mobile carriers. Wireline companies have a regulatory requirement to "port out". The regulatory requirement to "port in" has been a little more vague.  For example Google Voice will not port in your landline number because the process is more time consuming and cumbersome than porting in a mobile number. But any of the major mobile carriers; AT&T, Verizon, Sprint, etc.; will port in your landline number.  And as someone else said, you will either have to get a 2nd mobile or give up your current mobile number.

In 2003 the US FCC ruled landline numbers can be ported to wireless phones. In 2007 it ruled they can be ported to VoIP phones. I have read that Canadian numbers can be ported only within the same Local Interconnection Region (LIR) even though all Canada is a single LATA. You may not be able to port a number to the other side of town if the old and new accounts are with the same phone company. The law requires LNP when switching to another carrier. It is up to the phone company whether it allows you to port a number internally. The complicating factor is billing for interLATA calls on landlines.

The answer is (likely) yes.  This is known as LNP (local number portability).  It was mandated for carriers in the top 100 metro areas (US), so long as you are transferring to another local carrier.  Of course, that's the broad view, but yes, it can happen.