I go with the be lean advice. Spend as little as possible. Only spend money that is absolutely required to help you get the first sale.
The cellphone may or may not be in that category.
Other things may be a domain. For an MVP you can use a $1 for first year .info domain.
You don't need to pay for hosting, use Heroku or something on the free tier. Stationery and furniture can be free from friends / family that have too much. etc.
Live like a tramp.
Exception is if you are cashflow rich and time poor - i.e. you have a good job. Then you could invest into time saving tools and SaaS services (that you need to help you make the first sale more quickly). However such investments would still be a tiny fraction of the $10k. Actually it will be none of the $10k because you pay from your net salary.