I can confirm, this is causing me a major issue also (im operating primarily in a tourist town). I got around it by just entering + in the field, and a note to enter the phone number with country code minus the + symbol. However, I noticed signups reduced by around 50% after implementing this. An option with a dropdown country code field would be much better, and an option to lock the country code if the store wishes to operate as it is now. This would keep everybody happy.
For now my app is almost useless without the user being able to choose their country code.