Hi xcarlittosx! I want to make sure you are able to enjoy full speeds.
If you have the unlimited plus 2.5 GB hotspot feature your normal data on the phone should not be effected at all. If you have the unlimited with 2.5gb hotspot plan and your having issues with the internet on the phone itself I would contact T-Mobile for troubleshooting. Contact Us
If you have just the 2.5 GB plan without unlimited on the phone your speeds are going to drop to 2G even though the phone will show 4G. This will happen once you reach 2.5 GB. You can check your data usage by using #WEB# send.
Let me know if this helps
Nevin