Breaking the Chicken Egg dependency (taxi's vs travelers)

I have read through the Q&Z for chicken egg issue, on this site. And have come up with a solution. I hope to receive some business advice on my solution.

A Taxi Booking, webportal/mobile app is what I am building. Now, if you search for a taxi and get 0 search results, you will never use the app again. But if you get 10 taxi's all booked, then you will use the app again. Will you remain loyal to just this one system ? No, instead you will use what works for you when you need it. So its important to have taxi's in your system before you get your app out there for people to book space in them.

The question being, when I talk to taxi drivers, I need to convince them to

1. Purchase a mobile phone
2. Install my app (free)
3. Keep it online on a 2g connection (about 2$ per month), without expecting any business

I need about 3 months to build the customer base for customers to use and search for taxi's.

The challenge here is not point 1 and 2, since drivers who are "first adopters" will anyway register. The issue is keeping them on, until they start getting business. Basically keeping the interest alive.

Any techniques, or ideas that can help me "keep their interest alive". Now, keep in mind, I dont want to give them false booking information and do anything unethical here. I need to keep it truthful.

If my business idea is not working out, it should kinda reflect that.

Some ideas are

1. Get cab drivers to be my agents to register more cabs and convince their friends
2. Provide them with a ROI instead of duration, (I guess they will spend about 100 $ in 3 months). So until I get them business for 100km (assuming 1$ per km earned), I wont charge them for the service (with 6 month cap obviously).
3. Also if they get more people to register, they get 50km more.

Still thinking, I need to break this chicken-egg with a nice sales plan I guess. Any ideas ?

Edit :
Well, incentive to deregister kinda exists. A cab driver in (for example), India would not spend 100 Rs (2$) on something that wont get him back immediate value. If I dont communicate with them on a regular basis, they will just stop running the app. The question is what kinda information should I constantly share with them to keep their interest alive ?

Simple.... No Chicken, No Egg.. But No Egg, No Chicken.. (What if, You can make an egg in the incubator.. You solved the problem). Change your assumptions that the egg should come from the Chicken. Create the opportunity.

1. Most Cab drivers already have a Phone

2. Most can install your app

 And you said / confirmed, that you can get this done...

Now for the last part,

I assume you are not writing any exclusive agreements with the cab drivers, 

and you are not charging them to be registered on your site.

 a. There is no incentive for them to de-register.

 b. Ask them to keep the app installed, and try sending them business.

 If you add that extra incentive of MLM style signup's, you will get enough cab's on your

roll. and then when you got the critical mass, start thinking about exclusive contracts,

discounts, chargeup's or how ever you have decided to make the money from the cab drivers.

Their interest is "is the investment of my time worth it?", besides the fact of owning a mobile.
So, proof it and tell them your community is growing.

You could provide them success stories like how many apps installed, how many bookings accomplished or story of successful drivers.

And you could give early adopters some advantages. Or let them grow their advantages over time. This sort of gamification for keeping them interested in your app, until its a self-runner because of a huge community.

Edit: Check the story of german mytaxi.com to see and learn how they did it. Remarks: In Germany we usually have established callcenters doing the taxi booking for you. The mytaxi app disrupted this market successfully.

Regardless of the application roll-out process. I would begin capturing email addresses now for potential users and drivers. Then, when the time comes, you'll have a pool of interested people to notify.

The number of people willing to sign up for a "let me know when you go live" newsletter is probably greater than the number of folks willing to install software for a service not yet live.