Just wondering if it's possible to use the computer with a 3G/4G modem inside it to make telephone calls?

If so, are there any Linux software/dialers worth suggesting?

Short answer: yes.
Longer answer: Yes, but you don't want to.

3G/4G data will work just fine, and allow you to use something like Google Voice, Skype, or any other VOIP solution to make your phone calls. However, the latency and spotty performance isn't worth the effort. It just drops out too much to make it reliable, and the stuttering/echo is horrible. That said, Skype performs the best in such circumstances, at least in my experience. You can probably get a voice call to work with Skype over 3/4G, but it may not be the best quality.

I'm not talking about VOIP.

I want to use the notebook as one giant phone.

I've never tried it, and I'm not sure why anyone would want to either. Anyway, you might be interested in the following

http://wiki.freeswitch.org/wiki/GSMopen#What_Is_GSMopen

Good luck.

Then no, you can't. The built-in devices are (as you said) modems only. They don't support voice signals at all, unless you do VOIP, for the most part. There are a FEW devices that are voice-unlocked, but for the most part, they're not.

Even if they are, accomplishing this won't be easy, no matter what OS you use. You're essentially trying to simulate ALL the workings of the custom-built phone hardware/firmware via an emulator, while shoving real-time voice through the same set of software.

Firstly thanks for the tip.

To answer: Why would one want to?
The network provider issues a single sim on contract which has both voice call services and mobile broadband services combined. Hotswapping the sim between a conventional cell phone and the notebook for internet access would be a tedious and interruptive process. So I would really like to combine everything using the notebook.

I compiled Freeswitch and successfully loaded the GSMopen module. It loads up fine and the network provider is identified via the gsm list command.

Any idea how I can offset the voice calls to the soundcard?

While I understand your reasoning, the usual way to share the data is to tether the phone for internet sharing. The way to do this depends on the phone hardware, (which so far you haven't provided any details about). Most modern phones have wifi that can be configured as a hotspot (similar to a wireless router), allowing other devices (eg laptops) to connect for internet access. Some phones (eg my iPhone) also allow one to tether via a usb cable, and use 'cdc_ether' support to provide a network interface to the Linux OS.

I don't have any experience with using this software, so can't help further with this. Google may be your best friend here. That's how I found the link to freeswitch. Good luck.

Thanks.
Tethering is a possibility but isn't the correct way as a permanent solution.

Well, that's what most people would do, and consider to be the solution) In my work as a field engineer for a wireless broadband company, I occasionally have to gain internet connectivity via my phone using this method. If you want to pursue the freeswitch approach, that's up to you, (but I suspect few around here will have experience with it).

That's wrong. Tethering is only meant as a short term solution.
Well it depends on type of data service used. Even then most providers charge heavily for tethering.

With the advent of 4G there's no reason why Mobile BB can't replace traditional BB via lines and cables.

That's your opinion, and I won't waste time arguing about it. Tethering is just a means to and end that most would use when required. (I know of no one using freeswitch, and never heard of it until my google search brought it up.) Use what works for you.

Down to the service providers I guess, but not an issue here in NZ - restrictive measures like that would contravene our consumer laws. However, the data cap is not generous though (just a few GB per month IIRC), so I only use it when I have to.

I agree. Mobile BB offers offers obvious advantages with those of us on the move with tablets and phones, and fibre is not always viable to deploy for sparse populations anyway. It will only get better and more popular with technology and time.

Now this is going OT and not at all helpful to what the original query was about but,
I fail your understand your contradictive sentiments.

You agree Mobile BB is the way forwards yet you advocate it as a passive service via tethering. You agree with me that tethering is a means to and end and to be used as a means to an end. So?

Freeswitch can be tidied up but most importantly it proves that the principle can work. What's wrong with that?
Maybe next time you could report back on what you actually know and have experience of rather than throwing a hat into the ring and arguing senseless.

I thought I was clear enough. If you only have one mobile broadband device, then yes tethering is commonly used to share internet connectivity with other devices. Using a wireless broadband router with 3G support is another.

Nothing. Use what works for you. (I'll stick with what has worked for me for several years now.)

I didn't have to share any potential solutions with you. Maybe you need to show more appreciation for those trying to assist. I declared that I'd never tried it from the outset, but shared what I found in the hope that you could benefit. Don't alienate those trying to help. Accept that others won't necessarily agree with your approach either.

My USB 2G/3G dongles have proprietory software for Ubuntu 12. It supports sending SMS and using it as telephone as well.

Using python, pyserial I managed to make use of sending, receiving, reading sms's.

Good to know. Can you share the makes and models?