The short of this is:
No, you do not have to give any notice to your existing provider, however you may be subject to fees/termination charges depending upon the service(s). So not contacting your current provider can be costly and a major headache. However it can be easily avoided.
The long version, and details on the best way to change:
The process currently with changing from one provider to another for your services is that you should be contacting your current provider to cancel your existing services and then scheduling your new installation near the end of your existing service.
While providers often offer incentives to change, your existing provider may have a disconnection notice, or a contract that charges you out.
I -always- encourage reading your contract's fine print for cell phones, or
any equipment that you are purchasing/renting, not only for TV and Internet and
Cell phones, but really with anything that you purchase. (such as Computers,
Tv's, Car's, etc)
However if you are looking to transfer your Home phone service form one provider to another, you -must- leave that service active.
If you cancel that service then when the provider who wants to take that number over arranges to do so, they are told there is a pending order to cancel the service and their request is denied.
Then the install date comes and goes and nothing happens because the order was busted.
To clarify with an example:
-Provider A is your current home phone service.
-Provider B is whom you are transferring to.
-You contact Provider A and tell them you wish to cancel Phone, Tv and Internet. So they go through their process and arrange this.
-You contact Provider B and tell them you want to sign up and to bring over your Home phone number. They book an order and get ready to set you up with service.
-Provider B contacts Provider A to let them know to transfer the number, Provider A says No, because the Account holder has told them to cancel the service.
-Provider B then cancels their order as the request was denied, and by default assumes the Customer decided against getting the service.
For a smooth transition I would recommend this:
-Contact Provider A who is your current provider, tell them to cancel only the Internet and Tv.
-Contact Provider B, let them know you want their services and to bring your number over.
- Provider B then contacts Provider A and arranges to bring the service over on the installation date. The Phone service will end with Provider A on that date and the number will be carried over.
Often Providers can arrange to cancel all services for you, however this -DOES NOT- exempt you from any contracts or agreements that you have made with your current provider. If you have a Buyout or are required to provide a notice, then I urge you to look into this prior as providers can then charge you out for not providing them notice or arranging this.
If you are comfortable with this though, and would prefer to not have to contact your current provider, then the new provider will likely have a process to arrange the cancellation of your services for you, and they can arrange to cancel the Home phone, Internet, and TV service for you for the same date as your installation date of your new service.
As for the time for this to happen, providers require a minimum 4 Business days to transfer a phone number from one provider to another. So installation orders at minimum can be within 4 days, or up to 60 days into the future.
I hope this was able to answer your question, I again apologize for the length of this response, but I hope this gives you some insight so no matter if you are coming or going, things will go smoothly for you.