I use my phone a lot when traveling and recently switched to T-Mobile after being with AT&T forever. When AT&T got rid of their International Passport plans and wanted $10 a day I said no way.
A much better roaming deal with T-Mobile is their 15GB International Pass which gives you 15GB of high speed data over 30 days with unlimited texting and calling for $50 USD. I generally do 30 day trips so that comes to $1.67/day which can’t be beat IMO. And it works in Turkey according to T-Mobile. I’ll find out as I’ll be in Turkey in a couple weeks. Note: free 2G data is more restrictive in that respect