I have currently a 3BB internet connection which I plug into my router. But I also have an internet package on my phone with DTAC. Am I able to connect the PC to the phone's wireless internet so that I can cancel 3BB?

I'm using a PC with windows 7 and my phone is a Samsung S4.

Yes, go to settings and look for something like "tethering & mobile hotspot".

You can.

But what a magic mobile internet package do you have that would justify canceling a fixed line internet connection?

And what does not look quite clear to me:

does your PC have a WiFi adapter or not (because you write "plug into my router") ?

You can.

But what a magic mobile internet package do you have that would justify canceling a fixed line internet connection?

And what does not look quite clear to me:

does your PC have a WiFi adapter or not (because you write "plug into my router") ?

I don't exactly have a magical connection as it is with the 600 Baht 3BB package. Do you think it will be significantly slower if I go via the phone?

I have a wireless router but that's all. So I guess I need a wifi adaptor and then I'm ready to go?

You can also use the phone's USB cable to connect to your PC so ought to be easy enough to give it a try. My phone connection is better (faster) that my True cable/wifi connection. I only use it as a backup though as only have a 3GB monthly limit (at full speed).

I don't exactly have a magical connection as it is with the 600 Baht 3BB package.

Misunderstood.

I mean which data package at DTAC do you have?

For heavy use it will likely have a limit after which the transfer rate is throttled.

Do you think it will be significantly slower if I go via the phone?

I would expect so.

But as @Upnotover describes there must be exceptions to the rule.

DTAC will have a very limited bandwidth, typically 3GB or so for a low price.

Webpages on a mobile are typically lower bandwidth than those delivered to a PC.

So running both a mobile and a desktop on a mobile package will run through your package quickly.

Typically mobile packages are unlimited, but after your allowance they go to 2G speeds where you will be better walking to Singapore than waiting for pages load load.

Add to that the battery drain that running a wifi hotspot on a phone draws and your phone will be out of power and internet off in an hour.

Or charge your phone 24/7 and kill the battery in a few months.

In summary, wifi from landline will be a significantly superior experience all round.

Backup ok, but as primary usage you had better only check your emails once or twice a month.