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There's definitely nothing to this. It's not unusual for large companies to pay service providers to come in and install what are essentially microcells in buildings so that employees can make/receive calls in poor service areas.
Other way around. The service providers will pay you to have their equipment on your site. That's how it is in the UK, at least. They love to ask companies that have tallish buildings, from factories, towers, churches etc.
 
You still have to get permission from the city or county, and you can be sure there will be a group that shows up to protest it. Around here, they get a bus to take people to the hearings.

Don't forget that in certain neighborhoods the HOA (Home Owner's Association) will prevent things like TV antennas, satellite dishes, taller playground equipment...etc. from appearing on your property. I can't imagine ANY HOA allowing a home-mounted cell towers. Of course if your 'mansion' is on your own property, well away from anyone else you can do pretty much what you want...again assuming the local phone companies WANT to put up towers there.
 
I wish there was a T-Mobile iPhone, because I'm on WIND in Canada which uses the same AWS spectrum, and a no-contract iPhone would be a dream come true.
That is even less likely than a hybrid CDMA/three band HSPA\quad band GSM phone.

People like to bring up Verizon "world" phones but most of those phones only work in a few GSM countries since they don't support the same number of band that the iPhone does. CDMA carrier "world" phones barely work in Europe but fail to work in Japan.

I have used my Canadian iPhone 3GS in Japan on NTT DocoMo as well as carriers in the UK and continental Europe.
 
It's not unusual for multiple carriers to be collocated on the same pole and I would bet that the City of Cupertino required them to collocate.
 
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