To use N900 like a phone, without cellphone subscription . All you need is
1) Wifi
2) google voice account
3) gizmo5 account.

To receive incoming call:
6 blue squares>Settings>VoIP and IM acconts>New>
Sip
User name : gizmo5user@proxy01.sipphone.com
Password: gizmo5user password
Enabled check
Advanced settings (may skip if no dial out?)
User name gizmo5 user
Outbound proxy proxy01.sipphone.com
Port 5060
Done

New>
Google talk
User name gmail account user
Password gmail account password
Screen name anything
Save

Now you can receive incoming call thru your googlevoice number, when dial the googlevoice number your N900 rings, even when an earplug is in. Dont do it when in a wedding ceremony, your N900 will ring , loudly
More info to set up Gizmo5 and googlevoice (Grandcentral) here
Voice quality: Super!

To dial out:
1) Dialcentral, http://forums.internettablettalk.com...522&styleid=12, thread #887, #889 or
2) use your googlevoice dialout and set the phone to ring your gizmo5account

To dial out:
go to your googlevoice sign in, and enter the dial out number, your N900 should ring.
I have to use a desktop to do the googlevoice call. And it worked.

Voice quality: Super!

I know, this is pretty tricky and to people already has a cellphone subscription, it is not much. For me, this is another step to beefy up my N900, so that I can leave my N8x0 at home. Currently I am still carrying both, as I need the N8x0 to receive incoming call......... not any more, I can now leave my N8x0 at home, starting tomorrow

Enjoy,

bun

You have been warned: Once you set this up to receive incoming call, your N900 when online, will ring under almost ANY conditions, unbelievable. It will ring even when earplug is in, or when Lock screen and keys or when backup lite is out.

A nice trick to turn ringing off quick, put the N900 face down, it will stop ringing.

Again, the voice quality is much better than N8x0, so does the operation process, such as ring in and answering call etc

bun

Unfortunately, I couldn't send DTMF with my N900, whereas I could with the same setup (most of the time) on my N800. Sigh.

-jkq

Well, I bragged a little bit, I have some drug books on my N8x0 I am using on a daily bases and I am working now, as speaking, to make it to the N900, if not successful, I am still carrying both, in one shirt pocket, and my secretary had already questioned "What kind of steroid you are taking ... to make only one breast bigger?"

bun

What about when the Silent button is pushed in the power button menu?

It's not a steroid, it's MDD - Multiple Device Disorder.

-jkq

Good question: I just tried it, it still receives incoming call, but does not make the loud ring or vibration, you can still talk on the phone or use speaker.

bun

If it doesn't vibrate either, how do you know that you have an incoming call?

arnt those services only available in u.s or something. it wouldn't work for ppl in other countries

Your N900 switched into the phone UI, no matter what your N900 is doing. And if you hitting the speaker without thinking, the N900 will burst out "To receive call, press 1, to...." as loud as your speaker settings are,....again, very interesting if you are in the church and suppose to have your cell off

bun