The iPhone is pulling subscribers away from T-Mobile.

Now that all three of the bigger cellphone carriers have the iPhone, the country's number four cellphone company has even more customers leaving.

For the last two years, T-Mobile has been suffering from the loss of subscribers, and without the iPhone, that stream has turned into a flood.

T-Mobile says it lost 802,000 contract customers in the fourth quarter alone.

It also suffered the loss of "connected device" contracts.

T-Mobile's CEO promises the company will fight back with network upgrades.