Use of US cell phone in UK (O2 Sim)

#1
Last year I used a US based mobile phone in the UK. I bought an 02 Sim Card and was assigned a UK phone number. my Uber account switched to that number. I seem to remember receiving a message stating that this could be done only once. I would like to know if this is true or if I can switch my Uber account to a UK number and then back to the US number. Does anyone know?