Please upgrade the obi smartphone app to remain running in the background for the following cause.
After being told that an obi-app cannot receive an inbound call; I have discovered that if you install the android app and then call your soft-phone number that your android app will ring and you can answer the box caller. I then had another box user install an android app on his phone and from his cell phone obi-app we could call each other back and forth by dialing each others obi-soft-number.
This method allows peer to peer cell/wifi calling. However Obi does not support inbound calling to their android app and they developed the app to time out after a short interval once started. Their design is to have you start the app every-time you want to make an outbound call and then time itself out and shut -off after a few minutes.
I seems to me that it would be a very easy effort to (i) provide an option allowing the app to remain running in the background without timing itself off; and (ii) add an enhancement that on an incoming call the application will pop-up an option allowing the receiving end to answer or reject the call.
The feature you're describing can drain a smartphone's battery quickly. However, if you want to use it, there are already numerous third-party SIP clients for Android that support it, including the free CSIPSimple app, and the excellent Bria softphone from Counterpath.
I have always found the inability to run in the background to be the biggest flaw for that app. It's true it can be a battery hog but sometimes it's worth a little extra drain. Done correctly the battery use does not have to make a sip client unusable.
Both of the suggestions Steve made are good. I have used CsipSimple quite a bit and it worked great but I would like to add one more suggestion to the list. I have been using the new Grandstream Wave sip client and I really like it.
A sip client like the ones we suggested can do virtually everything Obion can. The only downside is that setup takes a little more time. After that they can be used seamlessly in conjunction with any Obi device.
My provider (VOIPO) allows "follow me" which will automatically call my cell phone if I don't answer my Obi desk phone. Additionally, for situations where I want to dial on my cellphone but have it seem as if I'm using my desk phone I have set up my cell phone set up as a trusted caller. Then I use Option 2 on the Auto Attendant to make my calls. For me this setup negates the need for a 3rd party SIP app and therefore saves my mobile phone battery.