The majority of Orange and T-Mobile customers with pay monthly contracts will be charged an extra 3.3 percent on their monthly deals from 10 April and 9 May respectively.
The two mobile brands are operated by Everything Everywhere, or EE. In similar statements issued separately Orange and T-Mobile said: "Due to inflation, which directly affects the costs of running our business, we've had to re-evaluate our prices and introduce an increase.
"All other charges outside your allowance, such as call costs, texts and bundles, stay the same."
In the case of Orange, those customers on pay monthly contracts signed prior to 1 February will pay the monthly increase.
Customers on the 30 day SIM Only, Mobile Broadband, and the new The Works and Animal consumer plans will not be affected by the increase. Orange says its business contract customers are also not being levied the increase.
With T-Mobile, customers on consumer or business pay monthly contracts will see their monthly price plans go up by the 3.3 percent from 9 May. Those signing up on or after 2 December 2012 will see the increase delayed until November 2013.
Customers on 30 day SIM Only, Mobile Broadband, and the recently launched Pay Monthly 24 month and Full Monty plans are also not affected by the increases, said T-Mobile.
Other mobile users will now be waiting to see whether the likes of Vodafone, O2 and Three put up their prices too this spring.