The biggest network that was affected by the error was O2, but also included other networks that rely on O2: GiffGaff, Sky Mobile, Lyca, and Tesco Mobile. The outage also resulted in customers being unable to make voice calls as the network became overloaded.
Pay as you go mobile broadband customers will get a 10% discount on a bolt on purchase in the new year - 02 will let notify when it is available.
A TfL spokesperson said: "We're sorry that customers are unable to use our Countdown screen at bus stops for live travel and some Santander Cycles customers can not hire bikes".
KitGuru Says: This is a particularly sore spot for those that suffered loss of earnings during the downtime, but I can't say it's been pleasant for anyone as an O2 customer myself.
"Our technical teams will continue to monitor service performance closely and we're starting the full review to understand what happened", it said.
"The faulty software that has caused these issues is being decommissioned and we apologise not only to our customers but also to their customers", he said.
O2 said it would update customers later on Friday on how "we will make yesterday's data service issue up to them".
O2 said its pay monthly customers and business and mobile broadband customers would be credited with two days of service by the end of January.
As the inquest into what happens begins, O2 and Ericsson which provides the software at the heart of the problem have issued joint apologies, but is still leaving customers guessing about compensation, for the moment.
The day-long O2 outage impacted all of the operator's 25 million customers, as well as an additional seven million customers using Sky Mobile, Tesco Mobile and giffgaff, all of which use the same mobile infrastructure.
'We fully appreciate it's been a poor experience and we are really sorry'. "We are working with our service provider to resolve this as soon as possible".
It is thought that a software issue in the system of the third party supplier led to the data outage.
She added: "The software is likely not open source, therefore, nobody other than Ericsson themselves was likely to be aware of it".