The original phrase is iced tea, and this spelling is still more common in print. Yet for many English speakers, ice tea more closely resembles the pronunciation, and this spelling has gained significant ground in 21st-century writing. There might still be some English speakers who consider it incorrect, but it is common in informal writing and is even making inroads in edited publications.
Other terms have undergone this shift. For example, ice cream and ice water were originally iced cream and iced water. Those are common terms, so there is certainly precedent for iced tea becoming ice tea. Yet for some reason iced tea has stuck around long after those terms lost the d. It could be simply that those terms are older and have had more time to change, while iced tea needs another decade or two to become ice tea.
Though iced tea remains more common, examples such as these are not hard to find:
Sipping on red raspberry ice tea instead of her usual hot coffee, Thongsy Singvongsa told me that when the temperatures climb, so do our spirits. [Chicago Tribune]
There was no crime here, just oodles of ice tea and raw carrot. [Telegraph]