The telcos, who connect phones to the network, promote their services using easily marketable handsets instead of competing on their own merits.
This is a horrible subversion of competition, and it destroys both markets. If handsets were sold by independant vendors, there would be a lot more room for "niche" customers, who like smaller phones, physical keyboards, long battery life or large screens for vision impaired. And if connectivity was sold in its own market, there would be room for subscriptions that don't bleed you dry when abroad, give you good coverage everywhere at a higher price or give you low price, but low coverage etc.
Instead we get just a few "one size fits all" models and subscriptions that favor the only the largest demographics.
Obligatory car analogy: If you want to buy a car, you have to get it from the oil company. Statoil have a good offer on Ford this month, but you can get a Fiat for "free" if you subscribe to BP's monthly refill service. And, of course, the car will not run if you fill it at a competing gas company.